PERITONEAL DIALYSIS SYSTEM

Abstract: Peritoneal dialysis systems and methods move liquid using a pump chamber (P1, P2) that is operated in response to pneumatic pressure variations applied by a pump actuator (PA1, PA2). The systems and methods periodically measure air pressures in the actuator (PA1, PA2) and an associated reference air chamber (VS1, VS2) and derive from these a measurement of liquid volume moved through the pump chamber (P1, P2). The systems and methods minimize derivation errors by compensating for temperature differences among the pump chamber (P1, P2); the pump actuator (PA1, PA2); and the reference chamber (VS1, VS2).

Description: Peritoneal dialysis system. Field of the Invention This invention relates to systems and meth¬ ods for performing peritoneal dialysis. Background of the Invention Peritoneal Dialysis (PD) periodically infuses sterile aqueous solution into the peritoneal cavity. This solution is called peritoneal dialysis solution, or dialysate. Diffusion and osmosis exchanges take place between the solution and the bloodstream across the natural body membranes. These exchanges remove the waste products that the kidneys normally excrete. The waste products typically consist of solutes like sodium and chloride ions, and the other compounds normally excreted through the kidneys like urea, creatinine, and water. The diffusion of water across the peritoneal membrane during dialysis is called ultrafiltration. Conventional peritoneal dialysis solutions include dextrose in concentrations sufficient to generate the necessary osmotic pressure to remove water from the patient through ultrafiltration. Continuous Ambulatory Peritoneal Dialysis (CAPD) is a popular form of PD. A patient performs CAPD manually about four times a day. During CAPD, the patient drains spent peritoneal dialysis solution from his/her peritoneal cavity. The patient then infuses fresh peritoneal dialysis solution into his/her peritoneal cavity. This drain and fill procedure usually takes about 1 hour. Automated Peritoneal Dialysis (APD) is an¬ other popular form of PD. APD uses a machine, called a cycler, to automatically infuse, dwell, and drain peritoneal dialysis solution to and from the patient's peritoneal cavity. APD is particularly attractive to a PD patient, because it can be performed at night while the patient is asleep. This frees the patient from the day-to-day demands of CAPD during his/her waking and working hours. The APD sequence typically last for several hours. It often begins with an initial drain cycle to empty the peritoneal cavity of spent dialysate. The APD sequence then proceeds through a succession of fill, dwell, and drain phases that follow one after the other. Each fill/dwell/drain sequence is called a cycle. During the fill phase, the cycler transfers a predetermined volume of fresh, warmed dialysate into the peritoneal cavity of the patient. The dialysate remains (or "dwells") within the peritoneal cavity for a time. This is called the dwell phase. During the drain phase, the cycler removes the spent dialysate from the peritoneal cavity. The number of fill/dwell/drain cycles that are required during a given APD session depends upon the total volume of dialyεate prescribed for the patient's APD regime. APD can be and is practiced in different ways. Continuous Cycling Peritoneal Dialysis (CCPD) is one commonly used APD modality. During each fill/dwell/drain phase of CCPD, the cycler infuses a prescribed volume of dialysate. After a prescribed dwell period, the cycler completely drains this liquid volume from the patient, leaving the peritoneal cavity empty, or "dry." Typically, CCPD employs 6 fill/dwell/drain cycles to achieve a prescribed therapy volume. After the last prescribed fill/dwell/drain cycle in CCPD, the cycler infuses a final fill volume. The final fill volume dwells in the patient through the day. It is drained at the outset of the next CCPD session in the evening. The final fill volume can contain a different concentration of dextrose than the fill volume of the successive CCPD fill/dwell/drain fill cycles the cycler provides. Intermittent Peritoneal Dialysis (IPD) is another APD modality. IPD is typically used in acute situations, when a patient suddenly enters dialysis therapy. IPD can also be used when a patient requires PD, but cannot undertake the responsibilities of CAPD or otherwise do it at home. Like CCPD, IPD involves a series of fill/dwell/drain cycles. The cycles in IPD are typically closer in time than in CCPD. In addition, unlike CCPD, IPD does not include a final fill phase. In IPD, the patient's peritoneal cavity is left free of dialysate (or "dry") in between APD therapy sessions. Tidal Peritoneal Dialysis (TPD) is another APD modality. Like CCPD, TPD includes a series of fill/dwell/drain cycles. Unlike CCPD, TPD does not completely drain dialyεate from the peritoneal cavity during each drain phase. Instead, TPD estab- lisheε a baεe volume during the firεt fill phase and drains only a portion of this volume during the first drain phase. Subsequent fill/dwell/drain cycles infuse then drain a replacement volume on top of the base volume, except for the last drain phase. The last drain phase removes all dialysate from the peritoneal cavity. There is a variation of TPD that includes cycles during which the patient is completely drained and infused with a new full base volume of dialysis. TPD can include a final fill cycle, like CCPD. Alternatively, TPD can avoid the final fill cycle, like IPD. APD offers flexibility and quality of life enhancements to a person requiring dialysis. APD can free the patient from the fatigue and inconvenience that the day to day practice of CAPD represents to some individuals. APD can give back to the patient his or her waking and working hours free of the need to conduct dialysis exchanges. Still, the complexity and size of past machines and associated disposables for various APD modalities have dampened widespread patient acceptance of APD as an alternative to manual peritoneal dialyεis methods. Summary of the Invention The invention provides improved systems and methods for performing peritoneal dialysis and the like. The systems and methods move liquid through a pump chamber that is operated in response to pnetimatic pressure variations applied by a pump actuator. The systemε and methodε periodically measure air pressures in the actuator and an associated reference air chamber and derive from these a measurement of liquid volume moved through the pump chamber. The systems and methods minimize derivation errors by compensating for temperature differences among the pump chamber; the pump actuator; and the reference chamber. According to one aspect of the invention, the systems and methods compensate for temperature differences by mounting the pump actuator and reference chamber as close to the pump chamber as possible. In a preferred embodiment, a peritoneal dialysis system comprises a liquid distribution cassette. The casεette has a pumping mechanism comprising a diaphragm associated with a pump chamber that communicates with the patient's peritoneal cavity. The system that embodies this aspect of the invention also includes an operating station for the cassette. The operating station contains a holder that retains the cassette. The operating chamber also includes a pressure transfer element that applies pneumatic pressure to the diaphragm within the holder to draw liquid into the pump chamber and to expel liquid from the pump chamber. The system includes a first mechanism that derives an initial air volume measurement V L after conveying pneumatic pressure to draw liquid into the pump chamber. The first mechanism also derives a final air volume measurement V £ after conveying pneumatic pressure to expel liquid from the pump chamber. The first mechanism includes a reference chamber having a known volume V, that is carried within the holder. Like the pressure transfer element, the reference chamber is exposed to generally the same temperature conditions aε the pumping mechanism itself. The first mechanism controls communication between the reference chamber and the pressure transfer element when liquid is drawn into the pump chamber and liquid is expelled from the pump chamber, as follows: (i) closing communication between reference chamber and the presεure tranεfer means to initialize the reference chamber to a measured initial air pressure (IP βl ) , while conveying a measured pressure to the preεεure tranεfer element (» i) 1 (ii) then opening communication between the reference chamber and the pressure transfer element to allow pressure equilibration at a measured new air pressure in the pressure transfer element (IP d2 ) and a measured new air presεure in the reference chamber (IP, 2 ) ; and (iϋ) then deriving the air volume measurement V 1 or V* aε followε: The system also includes a second mechanism that deriveε a measurement of liquid volume delivered (V d ) by the pumping chamber aε followε: V d - V £ - V t . In a preferred embodiment, the reference chamber carrieε within it an inεert for dampening pneumatic preεεure. The inεert iε preferably made of an open cell porouε material. The insert preferably includes a heat conducting material. According to another aspect of the invention, the syεtemε and methodε account for temperature differences among the pumping chamber; actuator; and reference chamber by applying a temperature correction factor (F t ) to the air volume of the reference chamber V, to derive a temperature- corrected reference air volume V, t , aε followε: V ■ F * V where: and where: C t is the absolute temperature of the cassette (expresεed in degreeε Rankine or Kelvin) , and R,. is the temperature of the reference chamber (expreεεed in the εame unitε aε C t ) . In a preferred embodiment, the systemε and methodε draw a volume of liquid to be pumped into the pumping chamber by applying negative preεεure to the pump actuator. An initial air volume V iε derived by: (i) retaining the initial liquid volume in the pumping chamber; (ii) initializing a reference chamber having a known air volume V, to a eaεured initial air pressure (IP ml ) , the reference chamber being first isolated from the pump actuator; (iii) applying the temperature correction factor (F t ) to the known air volume of the reference chamber V, to derive a temperature-corrected reference air volume V, t ; (iv) applying positive presεure to the pump actuator and meaεuring thiε air preεsure (IP dl ) ; (v) opening communication with the reference chamber to allow pressure equilibration and measuring the new air pressure in the pump actuator (IP d2 ) and the new air preεεure in the reference chamber (IP, 2 ) > and (vi) calculating V 1 aε follows: , = (IP θl - IP 32 ) * V. t _ (IP^ - IP dl ) . In this preferred embodiment, the systems and methodε then expel the volume of liquid from the pumping chamber by applying poεitive preεsure to the pump actuator. A final air volume V f is derived by: (i) retaining the final liquid volume in the pumping chamber; (ii) again initializing the reference chamber a measured initial air preεεure (FP sl ) , having firεt iεolated the reference chamber from the pump actuator chamber; (iii) again applying positive presεure to the pump actuator and meaεuring thiε air preεεure (FP dl ) ; (iv) again opening communication with the reference chamber to allow equilibration and measuring the new air presεure in the pump actuator (FP^) and the new air pressure in the reference chamber (FP, 2 ) ; and (v) calculating V l as follows: V, = (FP sl - FP, 2 ) * V, t _ (FP d2 - FP dl ) . Based upon the foregoing air volume derivationε, the systemε and methodε that embody thiε aεpect of the invention derive the liquid volume delivered (V d ) aε follows: V d = V f - V t . In one embodiment, the temperature correction factor F t is calculated as followε: F = C J^ where: C t iε the sensed absolute temperature of the pumping chamber (expresεed in degreeε Rankine or Kelvin) , and R t iε the sensed temperature of the reference chamber (expresεed in the same units as C t ) . Other features and advantages of the inventionε are set forth in the following specification and attached drawings. Brief Description of the Drawings Fig. 1 is a perspective view an automated peritoneal dialysis syεte that embodies the features of the invention, with the asεociated diεpoεable liquid delivery set ready for use with the associated cycler; Fig. 2 iε a perεpective view of the cycler associated with the system shown in Fig. 1, out of asεociation with the diepoεable liquid delivery set; Fig. 3 iε a perspective view of the diεpoεable liquid delivery εet and attached cassette that are aεεociated with the syεtem shown in Fig. 1; Figs. 4 and 5 are perspective views of the organizer that is associated with the set shown in Fig. 3 in the process of being mounted on the cycler; Figs. 6 and 7 are perεpective viewε of loading the diεpoεable caεεette attached to the set shown in Fig. 3 into the cycler for use; Fig. 8 is an exploded perεpective view of one side of the cassette attached to the disposable set shown in Fig. 3; Fig. 8A iε a plan view of the one side of the cassette shown in Fig. 8, showing the liquid paths within the caεεette; Fig. 8B iε a plan view of the other side of the cassette shown in Fig. 8, showing the pump chambers and valve stations within the cassette; Fig. 8C is an enlarged side section view of a typical casεette valve station shown in Fig. 8B; Fig. 9 is perspective view of the cycle shown in Fig. 2 with its housing removed to show its interior; Fig. 10 iε an exploded perεpective view εhowing the main operating moduleε houεed within the interior of the cycler; Fig. 11 iε an enlarged perεpective view of the cassette holder module houεed within the cycler; Figε. 12A and 12B are exploded views of the cassette holder module shown in Fig. 11; Fig. 13 iε a perεpective view of the operative front εide of the fluid pressure piεton houεed within the caεεette module shown in Fig. 11; Fig. 14A iε a perεpective view of the back εide of the fluid preεsure piston shown in Fig. 13; Fig. 14B is a perspective view of an alternative, preferred embodiment of a fluid pressure piεton that can be uεed with the εyεtem εhown in Fig. 1; Figε. 15A and 15B are top εectional viewε taken generally along line 15A-15A in Fig. 11, εhowing the interaction between the preεsure plate assembly and the fluid pressure piston within the module shown in Fig. 11, with Fig. 15A showing the pressure plate holding the piston in an at reεt position and Fig. 15B εhowing the preεsure plate holding the piεton in an operative poεition againεt the caεsette; Figs. 16A and 16B are side sectional view of the operation of the occluder assembly housed within the module shown in Fig. 11, with Fig. 16A showing the occluder asεembly in a poεition allowing liquid flow and Fig. 16B εhowing the occluder aεεembly in a position blocking liquid flow; Fig. 17 is a perspective view of the fluid pressure manifold module housed within the cycler; Fig. 18 is an exploded perspective view of interior of the fluid pressure manifold module shown in Fig. 17; Fig. 19 is an exploded perspective view of the manifold asεembly housed within the module shown in Fig. 18; Fig. 20 is a plan view of the interior of the base plate of the manifold aεεembly εhown in Fig. 19, εhowing the paired air portε and air conduction pathways formed therein; Fig. 21 is a plan view of the outside of the baεe plate of the manifold assembly shown in Fig. 19, also showing the paired air ports; Fig. 22 is an exploded perspective view of the attachment of a pneumatic valve on the outside of the baεe plate of the manifold asεembly εhown in Fig. 19, in regiεtry over a pair of air portε; Fig. 23 is a schematic view of the presεure supply system asεociated with the air regulation εystem that the manifold assembly εhown in Fig. 19 defineε; Fig. 24 is a schematic view of the entire air regulation εyεtem that the manifold aεεembly εhown in Fig. 19 defineε; Fig. 25 iε a flow chart showing the operation of the main menu and ultrafiltration review interfaceε that the controller for the cycler εhown in Fig. 1 employs; Fig. 26 iε a flow chart showing the operation of the therapy selection interfaces that the controller for the cycler εhown in Fig. 1 employs; Fig. 27 is a flow chart εhowing the operation of the set up interfaces that the controller for the cycler shown in Fig. 1 employs; Fig. 28 is a flow chart showing the operation of the run time interfaces that the controller for the cycler shown in Fig. 1 employs; Fig. 29 is a flow chart showing the operation of the background monitoring that the controller for the cycler shown in Fig. 1 employs; Fig. 30 is a flow chart εhowing the operation of the alarm routineε that the controller for the cycler εhown in Fig. 1 employe; Fig. 31 iε a flow chart showing the operation of the post therapy interfaceε that the controller for the cycler shown in Fig. 1 employs; Fig. 32 is a diagrammatic representation of εequence of liquid flow through the caeεette governed by the cycler controller during a typical fill phaεe of an APD procedure; Fig. 33 iε a diagrammatic representation of sequence of liquid flow through the cassette governed by the cycler controller during a dwell phase (replenish heater bag) of an APD procedure; Fig. 34 is a diagrammatic representation of εequence of liquid flow through the caεεette governed by the cycler controller during a drain phaεe of an APD procedure; and Fig. 35 iε a diagrammatic repreεentation of εequence of liquid flow through the caεεette governed by the cycler controller during a laεt dwell of an APD procedure. The invention may be embodied in several forms without departing from its spirit or eεεential characteristics. The scope of the invention is defined in the appended claims, rather than in the specific description preceding them. All em¬ bodiments that fall within the meaning and range of equivalency of the claims are therefore intended to be embraced by the claims. Description of the Preferred Embodiments Fig. 1 shows an automated peritoneal dialy¬ sis system 10 that embodies the features of the invention. The system 10 includes three principal components. These are a liquid supply and delivery set 12; a cycler 14 that interacts with the delivery set 12 to pump liquid through it; and a controller 16 that governs the interaction to perform a εelected APD procedure. In the illuεtrated and preferred embodiment, the cycler and controller are located within a common houεing 82. The cycler 14 iε intended to be a durable item capable of long term, maintenance free use. As Fig. 2 shows, the cycler 14 also presents a compact footprint, suited for operation upon a table top or other relatively small surface normally found in the home. The cycler 14 is also lightweight and por¬ table. The set 12 is intended to be a single use, disposable item. The user loads the set 12 on the cycler 14 before beginning each APD therapy session. The user removes the set 12 from the cycler 14 upon the completing the therapy sesεion and discardε it. In use (as Fig. 1 showε) , the user connects the εet 12 to hiε/her indwelling peritoneal catheter 18. The user also connects the set 12 to individual bags 20 containing sterile peritoneal dialysis εolution for infuεion. The set 12 also connects to a bag 22 in which the dialyεiε εolution is heated to a desired temperature (typically to about 37 degreeε C) before infuεion. The controller 16 paceε the cycler 14 through a prescribed series of fill, dwell, and drain cycles typical of an APD procedure. During the fill phaεe, the cycler 14 infuεeε the heated dialysate through the set 12 and into the patient's peritoneal cavity. Following the dwell phase, the cycler 14 institutes a drain phase, during which the cycler 14 discharges spent dialysis solution from the patient's peritoneal cavity through the set into a nearby drain (not εhown) . As Fig. 1 εhowε, the cycler 14 does not re¬ quire hangers for suspending the source solution bags 20 at a prescribed head height above it. Thiε iε becauεe the cycler 14 iε not a gravity flow εyεtem. Instead, uεing quiet, reliable pneumatic pumping action, the cycler 14 emulates gravity flow, even when the source solution bags 20 lie right alόngεide it, or in any other mutual orientation. The cycler 14 can emulate a fixed head height during a given procedure. Alternatively, the cycler 14 can change the head height to either in¬ crease or decreaεe the rate of flow during a proce- dure. The cycler 14 can emulate one or more εelected head height differentialε regardleεε of the actual head height differential exiεting between the patient'ε peritoneal cavity and the external liquid εourceε or destinations. Because the cycler 14 eεtabliεheε essentially an artificial head height, it haε the flexibility to interact with and adapt quickly to the particular phyεiology and relative elevation of the patient. The compact nature and εilent, reliable op- erating characteriεticε of the cycler 14 make it ideally suited for bedεide uεe at home while the patient iε aεleep. The principal system components will now be individually discusεed in greater detail. I. THE DISPOSABLE SET Aε Fig. 3 best shows, the εet 12 includeε a caεεette 24 to which lengths of flexible plaεtic tubeε 26/28/30/32/34 are attached. Fig. 3 showε the disposable liquid supply and delivery set 12 before it is readied for use in aεεociation with the cycler 14. Fig. 1 εhowε the diεpoεable set 12 when readied for use in asεociation with the cycler 14. In uεe (aε Fig. 1 εhows) , the distal ends of the tubes 26 to 34 connect outside the cycler 14 to the bags 20 of freεh peritoneal dialyεis solution, to the liquid heater bag 22, to the patient's indwelling catheter 18, and to a drain (not shown). For this reason, the tube 34 carries a con¬ ventional connector 36 for attachment to the patient's indwelling catheter 18. Other tubes 26/30/32 carry conventional connectorε 38 for attachment to bag portε. Tube 32 containε a Y- connector 31, creating tubing branches 32A and 32B, each of which may connect to a bag 20. The set 12 may contain multiple branches to accommodate attachment to multiple bags 20 of dialysis solution. The tube 28 has a drain connector 39. It serves to discharge liquid into the external drain (not shown) . The tubing attached to the set carries an inline, manual clamp 40, except the drain tube 28. Aε Figε. 1 and 3 show, the set 12 also preferably includes a branch connector 54 on the drain tube 28. The branch connector 54 creates a tubing branch 28A that carries a connector 55. The connector 55 attaches to a mating connector on an effluent inεpection bag (not shown) . Once attached, the patient can divert a volume (about 25 ml) of spent dialysate through branch 28A into the inspection bag during the first drain cycle. The bag allows the patient to inεpect for cloudy effluent, which iε an indication of peritonitiε. Aε Figε. 6 and 7 εhow, in use, the cassette 24 mounts inside a holder 100 in the cycler 14 (see Fig. 1, too) . The details of the holder 100 will be discussed in greater detail later. The holder 100 orients the casεette 24 for uεe vertically, aε Fig. 7 shows. As Figε. 3 to 5 εhow, the set 12 preferably in- eludes an organizer 42 that holds the distal tube ends in a neat, compact array. Thiε simplifies handling and shortenε the set up time. The organizer 42 includes a body with a serieε of slotted holders 44. The slotted holders 44 receive the diεtal tube ends with a friction fit. The organizer 42 includes εlot 46 that mateε with a tab 48 carried on outεide of the caεεette holder 100. A pin 50 on the outεide of the caεεette holder 100 also mates with an opening 52 on the organizer 42. These attach the organizer 42 and attached tube ends to the outεide of the caεεette holder 100 (aε Figε 1 and 5 show) . Once attached, the organizer 42 frees the uεer'ε handε for making the required connectionε with the other elements of the cycler 14. Having made the required connections, the user can remove and discard the organizer 42. The casεette 24 serves in asεociation with the cycler 14 and the controller 16 to direct liquid flow among the multiple liquid sources and destinations that a typical APD procedure requires. Aε will be described in greater detail later, the caεεette 24 provides centralized valving and pumping functionε in carrying out the εelected APD therapy. Figε. 8/8A/8B εhow the details of the casεette 24. Aε Fig. 8 shows, the casεette 24 includes an injection molded body having front and back sides 58 and 60. For the purpoεeε of description, the front εide 58 iε the εide of the caεεette 24 that, when the cassette 24 is mounted in the holder 100, faces away from the uεer. A flexible diaphragm 59 and 61 overlieε the front eide and back εideε 58 and 60 of the caεsette 24, respectively. The cassette 24 is preferably made of a rigid medical grade plastic material. The diaphragms 59/61 are preferably made of flexible sheets of medical grade plastic. The diaphragms 59/61 are sealed about their peripheries to the peripheral edgeε of the front and back εideε 58/60 of the caεεette 24. The caεεette 24 forms an array of interior cavitieε in the shapeε of wells and channels. The interior cavities create multiple pump chambers PI and P2 (visible from the front side 58 of the casεette 24, aε Fig. 8B showε) . The interior cavitieε alεo create multiple pathε Fl to F9 to convey liquid (viεible from the back side 60 of the casεette 24, as Figs. 8 and 8A εhowε) . The interior cavitieε alεo create multiple valve stations VI to V10 (viεible from the front εide 58 of the caεεette 24, aε Fig. 8B shows) . The valve stations VI to V10 interconnect the multiple liquid paths Fl to F9 with the pump chambers PI and P2 and with each other. The number and arrangement of the pump cham¬ bers, liquid pathε, and valve εtationε can vary. A typical APD therapy sesεion usually requires five liquid sources/deεtinations. The caεεette 24 that embodies the featureε of the invention provideε theεe connectionε with five exterior liquid lineε (i.e., the flexible tubes 26 to 32), two pump chamberε PI and P2, nine interior liquid pathε Fl to F9, and ten valve εtationε VI to Vlό. The two pump chamberε PI and P2 are formed aε wellε that open on the front εide 58 of the caεεette 24. Upεtanding edgeε 62 peripherally εurround the open wellε of the pump chamberε PI and P2 on the front εide 58 of the cassette 24 (see Fig. 8B) . The wells forming the pump chamberε PI and P2 are cloεed on the back εide 60 of the caεεette 24 (εee Fig. 8) , except that each pump chamber PI and P2 includes a vertically spaced pair of through holes or ports 64/66 that extend through to the back side 60 of the caεεette 24. Aε Figε. 8/8A/8B εhow, vertically εpaced portε 64(1) and 66(1) are aεεociated with pump chamber PI. Port 64(1) communicateε with liquid path F6, while port 66(1) communicateε with liquid path F8. Aε Figε. 8/8A/8B alεo εhow, vertically spaced portε 64(2) and 66(2) are aεεociated with pump chamber P2. Port 64(2) communicates with liquid path F7, while port 66(2) communicates with liquid path F9. As will become apparent, either port 64(1)/(2) or 66(1)/(2) can serve its aεεociated chamber P1/P2 aε an inlet or an outlet. Alternatively, liquid can be brought into and diεcharged out of the chamber P1/P2 through the εame port aeεociated 64(l)/(2) or 66(l)/(2). In the illustrated and preferred embodiment, the portε 64/66 are spaced so that, when the casεette 24 is oriented vertically for uεe, one port 64(1)/(2) iε located higher than the other port 66(1)/(2) associated with that pump chamber P1/P2. As will be described in greater detail later, this orientation provides an important air removal function. The ten valve stationε VI to ViO are likewiεe formed aε wellε open on the front side 58 of the cassette 24. Fig. 8C showε a typical valve εtation V κ . Aε Fig. 8C beεt εhowε, upεtanding edgeε 62 peripherally εurround the open wellε of the valve stations VI to V10 on the front side 58 of the casεette 24. Aε Fig. 8C beεt εhowε, the valve εtationε VI to V10 are cloεed on the back εide 60 of the cassette 24, except that each valve station V N includes a pair of through holes or portε 68 and 68' . One port 68 communicateε with a selected liquid path F„ on the back side 60 of the casεette 24. The other port 68' communicateε with another εelected liquid path F H . on the back side 60 of the casεette 24. In each valve εtation V„, a raised valve seat 72 surroundε one of the portε 68. Aε Fig. 8C beεt εhowε, the valve seat 72 terminates lower than the εurrounding peripheral edgeε 62. The other port 68' iε fluεh with the front εide 58 of the cassette. As Fig. 8C continueε to show best, the flexible diaphragm 59 overlying the front side 58 of the casεette 24 reεtε against the upstanding peripheral edges 62 surrounding the pump chamberε and valve stations. With the application of positive force uniformly against this side 58 of the cassette 24 (as shown by the f-arrows in Fig. 8C) , the flexible diaphragm 59 seats against the upstanding edges 62. The positive force forms peripheral seals about the pump chambers PI and P2 and valve stations VI to V10. This, in turn, isolateε the pump chamberε PI and P2 and valve stationε VI to V10 from each other and the reεt of the system. The cycler 14 applies poεitive force to the front caεεette side 58 for thiε very purpoεe. Further localized application of poεitive and negative fluid pressures upon the regions of the diaphragm 59 overlying theεe peripherally sealed areas serve to flex the diaphragm regions within these peripherally sealed areas. These localized applicationε of poεitive and negative fluid preεεureε on the diaphragm regionε overlying the pump chamberε PI and P2 serve to move liquid out of and into the chambers PI and P2. Likewise, these localized applications of positive and negative fluid presεure on the diaphragm regions overlying the valve εtationε VI to V10 will serve to seat and unseat these diaphragm regions againεt the valve εeatε 72, thereby cloεing and opening the aεεociated valve port 68. Fig. 8C εhowε in solid and phantom lines the flexing of the diaphragm 59 relative to a valve seat 72. In operation, the cycler 14 applies localized poεitive and negative fluid preεsures to the diaphragm 59 for opening and cloεing the valve portε. The liquid pathε Fl to F9 are formed aε elon- gated channelε that are open on the back side 60 of the cassette 24. Upstanding edgeε 62 peripherally surround the open channels on the back side 60 of the casεette 24. The liquid pathε Fl to F9 are cloεed on the front εide 58 of the caeεette 24, except where the channelε croεε over valve station ports 68/68'or pump chamber ports 64(l)/(2) and 66(l)/(2). The flexible diaphragm 61 overlying the back side 60 of the casεette 24 reεtε against the upstanding peripheral edges 62 surrounding the liquid paths Fl to F9. With the application of positive force uniformly against thiε side 60 of the casεette 24, the flexible diaphragm 61 εeatε against the upstanding edges 62. Thiε forms peripheral seals along the liquid paths Fl to F9. In operation, the cycler 14 also applies positive force to the diaphragm 61 for thiε very purpoεe. Aε Figε. 8/8A/8B εhow, five premolded tube connectors 27/29/31/33/35 extend out along one side edge of the cassette 24. When the cassette 24 iε vertically oriented for uεe, the tube connectorε 27 to 35 are vertically stacked one above the other. The firεt tube connector 27 iε the uppermoεt connector, and the fifth tube connector 35 iε the lowermoεt connector. Thiε ordered orientation of the tube connectorε 27 to 35 provideε a centralized, compact unit. It alεo makeε it possible to cluster the valve stations within the cassette 24 near the tube connectorε 27 to 35. The firεt through fifth tube connectorε 27 to 35 communicate with interior liquid pathε Fl to F5, reεpectively. Theεe liquid pathε Fl to F5 conεtitute the primary liquid pathε of the caεεette 24, through which liquid enterε or exitε the caεεette 24. The remaining interior liquid pathε F6 to F9 of the caεεette 24 conεtitute branch pathε that link the primary liquid pathε Fl to F5 to the pump chamberε PI and P2 through the valve εtationε VI to V10. Because the pump chambers PI and P2 are ver¬ tically oriented during uee, air entering the pump chamberε P1/P2 during liquid pumping operationε will accumulate near the upper port 64 in each pump chamber P1/P2. The liquid pathε Fl to F9 and the valve εta¬ tionε VI to V10 are purpoεefully arranged to iεolate the patient'ε peritoneal cavity from the air that the pump chamberε P1/P2 collect. They are alεo purpoεefully arranged eo that thiε collected air can be transferred out of the pump chambers P1/P2 during uεe. More particularly, the cassette 24 isolates selected interior liquid pathε from the upper portε 64 of the pump chamberε PI and P2. The casεette 24 thereby iεolateε theεe εelected liquid pathε from the air that accumulates in the pump chambers P1/P2. These air-iεolated liquid pathε can be used to convey liquid directly into and from the patient's peritoneal cavity. The casεette 24 also connects other selected liquid paths only to the upper portε 64(1)/(2) of the pump chamberε PI and P2. Theεe liquid pathε can be uεed to tranεfer air out of the reεpective pump chamber P1/P2. Theεe liquid pathε can also be used to convey liquid away from the patient to other connected elements in the εystem 10, like the heater bag 22 or the drain. In thiε way, the caεεette 24 serves to diεcharge entrapped air through eεtabliεhed noncritical liquid pathε, while iεolating the critical liquid pathε from the air. The cassette 24 thereby keeps air from entering the patient's peritoneal cavity. More particularly, valve stations VI to V4 serve only the upper ports 64(1)/(2) of both pump chambers PI and P2. These valve stations VI to V4, in turn, serve only the primary liquid paths Fl and F2. Branch liquid path F6 links primary paths Fl and F2 with the upper port 64(1) of pump chamber PI through valve stations VI and V2. Branch liquid path F7 links primary pathε Fl and F2 with the upper port 64(2) of pump chamber P2 through valve etationε V3 and V4. Theεe primary pathε Fl and F2 can thereby serve as noncritical liquid pathε, but not aε critical liquid paths, since they are not isolated from air entrapped within the pumping chambers P1/P2. By the εame token, the primary pathε Fl and F2 can serve to convey entrapped air from the pump chambers PI and P2. Tubes that, in uεe, do not directly convey liquid to the patient can be connected to the noncritical liquid pathε Fl and F2 through the upper two connectorε 27 and 29. One tube 26 conveyε liquid to and from the heater bag 22. The other tube 28 conveyε εpent peritoneal εolution to the drain. When conveying liquid to the heater bag 22 or to the drain, theεe tubes 26/28 can also carry air that accumulateε in the upper region of the pump chamberε P1/P2. In thiε arrangement, the heater bag 22, like the drain, serves as an air sink for the syεtem 10. Valve stations V5 to VIO serve only the lower portε 66(1)/(2) of both pump chamberε PI and P2. Theεe valve εtationε V5 to VIO, in turn, serve only the primary liquid pathε F3; F4; and F5. Branch liquid path F8 linkε primary paths F3 to F5 with the lower port 66(1) of pump chamber PI through valve stations V8; V9; and VIO. Branch liquid path F9 linkε primary pathε F3 to F5 with the lower port 66(2) of pump chamber P2 through valve εtationε V5; V6; and V7. Becauεe the primary pathε F3 to F5 are isolated from communication with the upper ports 64 of both pump chamberε PI and P2, they can serve as critical liquid pathε. Thuε, the tube 34 that conveyε liquid directly to the patient's indwelling catheter can be con¬ nected to one of the lower three connectors 31/33/35 (i.e., to the primary liquid paths F3 to F5) . The εame tube 34 alεo carrieε εpent dialyεate from the patient'ε peritoneal cavity. Likewiee, the tubeε 30/32 that carry εterile εource liquid into the pump chamberε enter through the lower pump chamber portε 66(1)/(2). Thiε arrangement makeε it unnecessary to incorporate bubble traps and air ventε in the tubing serving the casεette. The caεεette iε itε own εelf contained air trap. II. THE CYCLER As Figs. 9 and 10 beεt show, the cycler 14 carries the operating elements esεential for an APD procedure within a portable houεing 82 that occupieε a relatively εmall footprint area (aε Figε. 1 and 2 alεo show) . As already stated, the housing 82 encloεeε the cycle controller 16. The housing 82 also encloses a bag heater module 74 (see Fig. 9) . It further encloses a pneumatic actuator module 76. The pneumatic actuator module 76 also incorporates the cassette holder 100 already described, aε well as a failsafe liquid shutoff asεembly 80, which will be described later. The housing 82 also encloseε a source 84 of pneumatic pressure and an associated pneumatic pressure distribution module 88, which links the pressure source 84 with the actuator module 76. The housing 82 also encloεeε an AC power εupply module 90 and a back-up DC battery power εupply module 92 for the cycler 14. Further structural and functional details of theεe operating moduleε of the cycler 14 will be de- εcribed next. (A) The Baσ Heatinσ Module The bag heating module 74 includeε an exterior εupport plate 94 on the top of the cycler houεing 82 for carrying the heater bag 22 (aε Fig. 1 shows) . The support plate 94 is made of a heat conducting material, like aluminum. As Fig. 9 εhowε, the module 74 includeε a conventional electrical reεiεtance heating strip 96 that underlies and heats the support plate 94. Four thermocouples T1/T2/T3/T4 monitor the temperatures at εpaced locationε on the left, right, rear, and center of the heating strip 96. Fifth and sixth thermocouples T5/T6 (see Figs. 2 and 10) independently monitor the temperature of the heater bag 22 itεelf. A circuit board 98 (εee Fig. 9) receiveε the output of the thermocoupleε Tl to T6. The board 98 conditionε the output before tranεmitting it to the controller 16 for processing. In the preferred embodiment, the controller 16 includes a heater control algorithm that elevates the temperature of liquid in the heater bag 22 to about 33 degreeε C before the first fill cycle. A range of other safe temperature settingε could be used, which could be selected by the user. The heating continues as the first fill cycle proceeds until the heater bag temperature reacheε 36 degreeε C. The heater control algorithm then maintainε the bag temperature at about 36 degreeε C. The algorithm functions to toggle the heating strip 96 on and off at a senεed plate temperature of 44 degreeε C to aεεure that plate temperature never exceedε 60 degreeε C. (B) The Pneumatic Actuator Module The caεεette holder 100, which forms a part of the pnetimatic actuator module 76, includeε a front plate 105 joined to a back plate 108 (εee Fig. 12A) . The plateε 105/108 collectively form an interior receεε 110. A door 106 iε hinged to the front plate 105 (εee Figε. 6 and 7). The door 106 moveε between an opened poεition (εhown in Figs. 6 and 7) and a cloεed poεition (εhown in Figε. 1; 2; and 11). A door latch 115 operated by a latch handle 111 contactε a latch pin 114 when the door 106 iε cloεed. Moving the latch handle 111 downward when the door 106 iε closed engages the latch 115 to the pin 114 to lock the door 106 (aε Figε. 4 and 5 εhow) . Moving the latch handle 111 upward when the door 106 iε closed releaseε the latch 115 from the pin 114. This allows the door 106 to be opened (aε Fig. 6 εhowε) to gain acceεε to the holder interior. With the door 106 opened, the uεer can inεert the caεεette 24 into the receεε 110 with itε front side 58 facing the interior of the cycler 14 (as Figs. 6 and 7 show) . The inside of the door 106 carries an upraised elastomeric gaεket 112 poεitioned in oppoεition to the receεε 110. Cloεing the door 106 bringε the gasket 112 into facing contact with the diaphragm 61 on the back side 60 of the cassette 24. The pneumatic actuator module 76 contains a pneumatic piston head aεεembly 78 located behind the back plate 108 (εee Fig. 12A) . The piεton head aεεembly 78 includeε a piεton element 102. Aε Figε. 12A; 13 and 14 show, the piston element 102 comprises a molded or machined plastic or metal body. The body containε two pump actuatorε PAl and PA2 and ten valve actuatorε VA1 to VA10. The pump actuatorε PA1/PA2 and the valve actuatorε VA1 to VA10 are mutually oriented to form a mirror image of the pump εtationε P1/P2 and valve stations VI to V10 on the front εide 58 of the caεεette 24. Each actuator PA1/PA2/VA1 to VA10 includeε a port 120. The portε 120 convey poεitive or negative pneumatic preεεureε from the pneumatic preεεure diεtribution module 88 (as will be described in greater detail later) . As Fig. 13 best shows, interior grooveε 122 formed in the pieton element 102 εurround the pump and valve actuatorε PA1/PA2/VA1 to VA10. A preformed gaεket 118 (see Fig. 12A) fitε into theεe grooves 122. The gasket 118 seals the peripheries of the actuatorε PA1/PA2/VA1 to VA10 againεt pneumatic preεsure leaks. The configuration of the preformed gasket 118 followε the pattern of upεtanding edgeε that peripherally surround and separate the pump chambers PI and P2 and valve εtationε VI to VIO on the front εide 58 of the caεεette 24. The piεton element 102 iε attached to a preεεure plate 104 within the module 76 (εee Fig. 12B) . The preεεure plate 104 iε, in turn, supported on a frame 126 for movement within the module 76. The side of the plate 104 that carries the piston element 102 abuts against a resilient spring element 132 in the module 76. In the illustrated and preferred embodiment, the spring element 132 iε made of an open pore foam material. The frame 126 alεo εupportε an inflatable main bladder 128. The inflatable bladder 128 contactε the other side of the plate 104. The piston element 102 extends through a window 134 in the εpring element 132 (see Fig. 12A) . The window 134 regiεterε with the caεεette receiving receεε 110. With a caεεette 24 fitted into the receεε 110 and the holder door 106 cloεed, the piεton element 102 in the window 134 iε mutually aligned with the diaphragm 59 of the caεsette 24 in the holder receεε 110. Aε Fig. 15A εhowε, when the main bladder 128 iε relaxed (i.e., not inflated), the spring element 132 contactε the plate 104 to hold the piεton element 102 away from preεεure contact with a cassette 24 within the holder recesε 110. Aε will be deεcribed in greater detail later, the pneumatic preεεure diεtribution module 88 can supply poεitive pneumatic preεεure to the main bladder 128. This inflates the bladder 128. As Fig. 15B shows, when the main bladder 128 inflates, it presseε the plate 104 against the spring element 132. The open cell structure of the spring element 132 resiliently deforms under the preεεure. The piston element 102 moveε within the window 134 into preeεure contact againεt the caeεette diaphragm 59. The bladder pressure presεeε the piεton element gasket 118 tightly against the casεette diaphragm 59. The bladder preεεure alεo preεεeε the back εide diaphragm 61 tightly againεt the interior of the door gaεket 112. Aε a reεult, the diaphragms 59 and 61 seat against the upstanding peripheral edgeε 62 that εurround the caεεette pump chamberε P1/P2 and valve εtationε VI to VIO. The preεεure applied to the plate 104 by the bladder 128 βealε the peripherieε of these regions of the caβεette 24. The piston element 102 remains in thiε operating poεition aε long aε the main bladder 128 retains positive presεure and the door 106 remainε cloεed. In thiε poεition, the two pump actuatorε PAl and PA2 in the piεton element 102 regiεter with the two pump chamberε PI and P2 in the caεεette 24. The ten valve actuatorε VAl to VA10 in the piεton element 102 likewiεe register with the ten valve εtationε VI to V10 in the cassette 24. As will be deεcribed in greater detail later, the pneumatic preεεure diεtribution module 88 conveyε poεitive and negative pneumatic fluid preεsure to the actuatorε PA1/PA2/VA1 to VAIO in a εequence governed by the controller 16. Theεe poεitive and negative preεεure pulεeε flex the dia¬ phragm 59 to operate the pump chamberε P1/P2 and valve stations VI to VIO in the casεette 24. This, in turn, moves liquid through the casεette 24. Venting the positive presεure in the bladder 128 relieveε the preεεure the plate 104 applies to the casεette 24. The resilient spring element 132 urges the plate 104 and attached piston element 102 away from pressure contact with the casεette diaphragm 59. In thiε poεition, the door 106 can be opened to unload the caεεette 24 after uεe. Aε Fig. 12A εhowε, the gaεket 118 preferably includeε an integral elastomeric membrane 124 stretched acroεε it. Thiε membrane 124 iε expoεed in the window 134. It εerveε as the interface between the piεton element 102 and the diaphragm 59 of the cassette 24, when fitted into the holder receεε 110. The membrane 124 includeε one or more small through holeε 125 in each region overlying the pump and valve actuatorε PA1/PA2/VA1 to VA10. The holeε 125 are eized to convey pneumatic fluid pressure from the piεton element actuatorε to the caεεette diaphragm 59. Nevertheleεε, the holes 125 are small enough to retard the pasεage of liquid. Thiε forms a flexible eplaεh guard across the expoεed face of the gaεket 118. The splash guard membrane 124 keeps liquid out of the pump and valve actuatore PA1/PA2/VA1 to VA10, εhould the caεεette diaphragm 59 leak. The εplaεh guard membrane 124 alεo εerveε aε a filter to keep particulate matter out of the pump and valve actuatorε of the piεton element 102. The splash guard membrane 124 can be periodically wiped clean when casεetteε are exchanged. Aε Fig. 12A shows, inserts 117 preferably occupy the pump actuators PAl and PA2 behind the membrane 124. In the illustrated and preferred embodiment, the inserts 117 are made of an open cell foam material. The insertε 117 help dampen and direct the pneumatic preεεure upon the membrane 124. The presence of insertε 117 stabilizeε air preεεure more quickly within the pump actuatorε PAl and PA2, helping to negate tranεient thermal effectε that arise during the conveyance of pneumatic pressure. (C) The Liquid Shutoff Assembly The liquid shutoff asεembly 80, which forms a part of the pneumatic actuator module 76, serves to block all liquid flow through the casεette 24 in the event of a power failure or another deεignated error condition. As Fig. 12B shows, the liquid shutoff assembly 80 includes a movable occluder body 138 located behind the preεεure plate frame 126. The occluder body 138 haε a εide hook element 140 that fitε into a slot 142 in the presεure plate frame 126 (εee Figε. 16A/B) . Thiε hook-in-εlot fit eεtabliεheε a contact point about which the occluder body 138 pivotε on the presεure plate frame 126. The occluder body 138 includeε an elongated occluder blade 144 (see Figs. 12A; 15; and 16). The occluder blade 144 extendε through a slot 146 in the front and back plates 105/108 of the holder 100. When the holder door 106 is closed, the blade 144 faces an elongated occluder bar 148 carried on the holder door 106 (see Figε. 15 and 16). When the caεεette 24 occupieε the holder receεε 110 (see Fig. 7) and the holder door 106 is closed, all tubing 26 to 34 attached to the caεsette 24 paεεeε between the occluder blade 144 and the occluder bar 148 (aε Figε. 15 and 16 show) . In the illustrated and preferred embodiment, a region 145 of the flexible tubing 26 to 34 is held in a mutually close relationship near the casεette 24 (εee Fig. 3) . Thiε bundled tubing region 145 further simplifies the handling of the casεette 24. Thiε bundled region 145 alεo arrangeε the cassette tubing 26 to 34 in a close, side by side relationship in the region between the occluder blade 144 and bar 148 (see Fig. 7) . In the illustrated and preferred embodiment, the εidewallε of the flexible tubing 26 to 34 are RF surface welded together to form the bundled region 145. Pivotal movement of the occluder body 138 moves the occluder blade 144 toward or away from the occluder bar 148. When spaced apart (as Fig. 16A showε) , the occluder blade and bar 144/148 allow clear paεεage of the caεεette tubing 26 to 34. When brought together (aε Fig. 16B εhowε) , the occluder blade and bar 144/148 crimp the caεεette tubing 26 to 34 cloεed. Occluder springs 150 carried within εleeves 151 normally bias the occluder blade and bar 144/148 together. An occluder bladder 152 occupieε the εpace between the occluder body 138 and the frame 126 (εee Fig. 12B) . Aε Fig. 16B εhowε, when the occluder bladder 152 iε relaxed (i.e., not inflated), it makeε no contact againεt the occluder body 138. The occluder springs 150 urge the occluder blade and bar 144/148 together, simultaneouεly crimping all casεette tubing 26 to 34 cloεed. Thiε preventε all liquid flow to and from the cassette 24. As will be described in greater detail later, the pneumatic pressure diεtribution module 88 can εupply positive pneumatic presεure to the occluder bladder 152. This inflates the bladder 128. As Fig. 16A shows, when the occluder bladder 152 inflates, it presεeε againεt the occluder body 138 to pivot it upward. Thiε moveε the occluder blade 144 away from the occluder bar 158. Thiε permits liquid to flow through all tubing to and from the cassette 24. The occluder blade and bar 144/148 remain spaced apart as long aε the occluder bladder 152 re¬ tains poεitive preεεure. Venting of poεitive preεεure relaxeε the occluder bladder 152. The occluder springs 150 immediately urge the occluder blade and bar 144/148 back together to crimp the tubing closed. As will be described in greater detail later, an electrically actuated valve C6 communicateε with the occluder bladder 152. When receiving electrical power, the valve C6 iε normally closed. In the event of a power losε, the valve C6 openε to vent the occluder bladder 152, crimping the caεsette tubing 26 to 34 cloεed. The aεsembly 80 provides a pneumatically actuated fail-safe liquid shut off for the pneumatic pumping system. (D) The Pneumatic Pressure Source The pneumatic presεure εource 84 comprises a linear vacuum pump and air compresεor capable of generating both negative and poεitive air preεεure. In the illuεtrated and preferred embodiment, the pump 84 iε a conventional air co preεεor/vacuum pump commercially available from Medo Corporation. Aε Fig. 23 shows, the pump 84 includes an inlet 154 for drawing air into the pump 84. The pump inlet 154 supplieε the negative preεεure required to operate the cycler 14. Aε Fig. 23 alεo shows, the pump 84 also includes an outlet 156 for discharging air from the pump 84. The pump outlet 156 supplies positive preεεure required to operate the cycler 14. Figε. 9 and 10 also εhow the inlet 154 and outlet 156. The pump inlet 154 and the pump outlet 156 communicate with ambient air via a common vent 158 (ehown εchematically in Fig. 23) . The vent 158 in- cludeε a filter 160 that removeε particulateε from the air drawn into the pump 84. (E) The Pressure Distribution System Figs. 17 to 22 εhow the detailε of the pneumatic preεεure diεtribution module 88. The module 88 encloεeε a manifold aεεembly 162. The manifold aεsembly 162 controlε the diεtribution of poεitive and negative preεεureε from the pump 84 to the piεton element 102, the main bladder 128, and the occluder bladder 152. The controller 16 provideε the command signals that govern the operation of the manifold asεembly 162. Aε Figε. 18 shows, a foam material 164 preferably lines the interior of the module 88 encloεing the manifold aεεembly 162. The foam material 164 provideε a barrier to dampen sound to asεureε quiet operation. Aε Figε. 18 and 19 show, the manifold asεembly 162 includeε a top plate 166 and a bottom plate 168. A εealing gaεket 170 is sandwiched between the plateε 166/168. The bottom plate 168 (see Figs. 20 and 21) includes an array of paired air portε 172. Fig. 20 εhowε the inside surface of the bottom plate 168 that faces the gasket 170 (which is designated IN in Figs. 19 and 20). Fig. 21 shows the outside surface of the bottom plate 168 (which is designated OUT in Figε. 19 and 21) . The inεide εurface (IN) of the bottom plate 168 alεo contains an array of interior grooveε that form air conduction channelε 174 (see Fig. 20) . The array of paired air ports 172 communicates with the channels 174 at spaced intervals. A block 176 fastened to the outside surface (OUT) of the bottom plate 168 contains an additional air conduction channelε 174 that communicate with the channelε 174 on the inεide plate surface (IN) (see Figs. 19 and 22) . Tranεducerε 178 mounted on the exterior of the module 88 sense through associated senεing tubes 180 (see Fig. 18) pneumatic pressure conditions present at various pointε along the air conduction channelε 174. The transducers 178 are conventional semi¬ conductor piezo-resiεtance preεεure senεorε. The top of the module 88 includeε εtand-off pinε 182 that carry a board 184 to which the preεεure tranεducerε 178 are attached. The outεide surface (OUT) of the bottom plate 168 (see Figs. 19 and 22) carries a solenoid actuated pneumatic valves 190 connected in communication with each pair of air ports 172. In the illustrated embodiment, there are two rows of valves 190 arranged along opposite εideε of the outεide surface (OUT) of the plate 168. Twelve valveε 190 form one row, and thirteen valveε 190 form the other row. Aε Fig. 22 shows, each pneumatic valve 190 is attached in communication with a pair of air ports 172 by screwε fastened to the outεide εurface (OUT) of the bottom plate 168. Aε Figε. 19 and 22 alεo εhow, each valve 190 iε electrically connected by ribbon cableε 192 to the cycler controller 16 by contactε on a junction board 194. There are two junction boardε 194, one for each row of valveε 190. Each pneumatic valve 190 operateε to control air flow through itε aεεociated pair of portε 172 to link the porte 172 to the variouε air channelε 174 the bottom plate 168 carrieε. Aε will be deεcribed in greater detail later, εome of the valveε 190 are conventional three way valveε. Otherε are conventional normally cloεed two way valveε. The air channele 174 within the manifold aεεembly 162 are coupled by flexible tubing 196 (εee Fig. 17) to the εyεtem componentε that operate using pneumatic presεure. Slotε 198 in the εide of the module 88 accommodate the paεεage of the tubing 196 connected to the manifold aεεembly 162. Figε. 9 and 10 also show the flexible tubing 196 that linkε the manifold aεεembly 162 to the pneumatically actuated and controlled εyεtem componentε. Fig. 11 further εhowε the tubing 196 from the manifold aεεembly 162 entering the pneumatic actuator module 76, where they connect to the main bladder 128, the occluder bladder 152, and the piεton element 102. Fig. 14A further εhowε the T- fittingε that connect the tubing 196 to the portε of the valve actuatorε VAl to VA10 and the ports of the pump actuators PA1/PA2 of the piston element 102. These connectionε are made on the back side of the piεton element 102. 1. The Pressure Regulation System The air conduction pasεageε 174 and the flexible tubing 196 aεεociated with the manifold assembly 162 define a fluid presεure regulation system 200 that operates in reεponεe to command signals from the cycler controller 16. Figs. 23 and 24 show the details of the air regulation system 200 in schematic form. In response to the command signals of the controller 16, the pressure regulation system 200 directs the flow of positive and negative pneumatic pressures to operate the cycler 14. When power is applied, the syεtem 200 maintainε the occluder aεεembly 80 in an open, flow-permitting condition; it seals the casεette 24 within the holder 100 for operation; and it conveyε pneumatic preεεure to the piεton element 102 to move liquid through the caεsette 24 to conduct an APD procedure. The presεure regulation syεtem 200 also provides in¬ formation that the controller 16 processes to measure the volume of liquid conveyed by the casεette 2 . a. Pressure Supply Network Aε Fig. 23 shows, the regulation system 200 includes a presεure supply network 202 having a poεitive preεεure side 204 and a negative presεure side 206. The poεitive and negative preεεure sides 204 and 206 can each be selectively operated in either a low-relative presεure mode or high-relative preεεure mode. The controller 16 callε for a low-relative preεsure mode when the cycler 14 circulates liquid directly through the patient'ε indwelling catheter 18 (i.e., during patient infueion and drain phaεeε) . The controller 16 callε for a high-relative pressure mode when the cycler 14 circulates liquid outside the patient's indwelling catheter 18 (i.e., during transferε of liquid from supply bags 20 to the heater bag 22) . In other words, the controller 16 activates the low-relative preεεure mode when conεiderationε of patient comfort and εafety predominate. The controller 16 activates the high-relative presεure mode when conεiderationε of proceεεing speed predominate. In either mode, the pump 84 draws air under negative preεεure from the vent 158 through an inlet line 208. The pump 84 expelε air under poεitive preεεure through an outlet line 210 to the vent 158. The negative pressure supply side 206 commu¬ nicates with the pump inlet line 208 through a nega- tive presεure branch line 212. The three way pneumatic valve DO carried on the manifold aεεembly 162 controlε thiε communication. The branch line 212 εupplieε negative preεεure to a reεervoir 214 carried within the cycler houεing 82 (thiε can be εeen in Figε. 9 and 10) . The reεervoir 214 preferably haε a capacity greater than about 325 cc and a collapse preεεure of greater than about -10 pεig. The transducer XNEG carried on the manifold aεεembly 162 senseε the amount of negative preεεure stored within the negative pressure reservoir 214. When in the high-relative negative presεure mode, the tranεducer XNEG tranεmitε a control signal when the predefined high-relative negative presεure of -5.0 pεig iε εenεed. When in the low-relative negative preεεure mode, the transducer XNEG transmitε a control εignal when the predefined low- relative negative preεεure of -1.2 pεig is sensed. The preεεure reεervoir 214 serves aε both a low- relative and a high-relative preεεure reservoir, depending upon the operating mode of the cycler 14. The positive preεεure supply side 204 commu¬ nicates with the pump outlet line 210 through a main poεitive preεεure branch line 216. The three way pneumatic valve C5 controlε thiε communication. The main branch line 216 supplieε positive presεure to the main bladder 128, which seats the piston head 116 against the casεette 24 within the holder 100. The main bladder 128 also εerveε the εyεtem 202 aε a poεitive high preεεure reεervoir. The main bladder 128 preferably haε a capacity of greater than about 600 cc and a fixtured burεt preεεure over about 15 pεig. Tranεducer XHPOS carried on the manifold aεεembly 162 senses the amount of positive presεure within the main bladder 128. Tranεducer XHPOS tranεmitε a control εignal when the predetermined high-relative preεsure of 7.5 pεig is senεed. A firεt auxiliary branch line 218 leadε from the main branch line 216 to a εecond poεitive preεεure reεervoir 220 carried within the houεing 82 (which can also be seen in Figs. 9 and 10) . The two way, normally closed pneumatic valve A6 carried by the manifold assembly 168 controlε the passage of poεitive preεsure to the second reservoir 220. The second reservoir 220 serves the system 202 as a reservoir for low-relative positive presεure. The second reservoir 220 preferably haε a capacity of greater than about 325 cc and a fixtured burεt pressure greater than about 10 pεig. Tranεducer XLPOS carried on the manifold assembly 162 senseε the amount of poεitive preεεure within the εecond preεεure reservoir 220. Transducer XLPOS iε εet to tranεmit a control signal when the predetermined low-relative preεsure of 2.0 psig is sensed. The valve A6 divides the poεitive preεεure εupply side 204 into a high-relative positive preεεure region 222 (between valve station C5 and valve station A6) and a low-relative positive presεure region 224 (between valve εtation A6 and the εecond reservoir 220) . A second auxiliary poεitive preεεure branch line 226 leadε from the main branch line 216 to the occluder bladder 152 through three way pneumatic valve C6. The occluder bladder 152 alεo serves the syεtem 202 aε a poεitive high pressure reservoir. A bypass branch line 228 leads from the main branch 216 to the vent 158 through the two way, nor- mally cloεed valve A5. The valve C6 alεo communicateε with the bypass branch line 228. The preεεure supply network 202 has three modeε of operation. In the firεt mode, the network 202 εupplieε the negative preεεure εide 206. In the εecond mode, the network 202 εupplieε the poεitive preεεure εide 204. In the third mode, the network 202 εupplieε neither negative or poεitive preεεure εide 204/206, but serves to circulate air in a continuous manner through the vent 158. With the three modeε of operation, the pump 84 can be continuouεly operated, if deεired. Thiε avoids any time delayε and noiεe occaεioned by cycling the pump 84 on and off. In the firεt mode, valve εtation DO openε communication between the negative branch line 212 and the pump inlet line 208. Valve C5 openε communication between the pump outline line 210 and the vent 158, while blocking communication with the main poεitive branch line 216. The pump 84 operateε to circulate air from the vent 158 through itε inlet and outlet lines 208/210 to the vent 158. This circulation also draws air to generating negative presεure in the negative branch line 212. The reεervoir 214 εtoreε thiε negative preεεure. When the transducer XNEG senseε its prede¬ termined high-relative or low-relative negative presεure, it εupplieε a command εignal to operate valve DO, cloεing communication between the pump inlet line 208 and the negative branch line 212. In the second mode, valve DO closee communi¬ cation between the negative branch line 212 and the pump inlet line 208. Valve C5 cloεeε communication with the vent 158, while opening communication with the main poεitive branch line 216. The pump 84 operateε to convey air under poεitive preεεure into the main poεitive branch line 216. Thiε positive presεure accumulates in the main bladder 128 for conveyance to the pump and valve actuatorε on the piεton element 102. By operating three way valve C6, the poεitive preεεure can also be directed to fill the occluder bladder 152. When the valve C6 is in thiε poεition, the poεitive preεεure in the occluder bladder 152 alεo can be conveyed to the pump and valve actuatorε on the piεton element 102 Otherwise, valve C6 directs the positive pressure through the bypasε line 228 to the vent 158. In the abεence of an electrical signal (for example, if there is a power failure) , valve C6 openε the occluder bladder 152 to the bypaεε line 228 to the vent 158. Valve A6 iε either opened to convey air in the main branch line 216 to the low preεεure reeervoir 214 or cloεed to block thiε conveyance. The transducer XLPOS opens the valve A6 upon sensing a preεεure below the low-relative cut-off. The tranεducer XLPOS cloεeε the valve station A6 upon sensing presεure above the low-relative cut-off. The tranεducer XHIPOS operateε valve C5 to cloεe communication between the pump outlet line 210 and the main poεitive branch line 216 upon εenεing a preεεure above the high-relative ' cut-off of 7.5 pεig. In the third mode, valve DO cloεeε communi¬ cation between the negative branch line 212 and the pump inlet line 208. Valve C5 openε communication between the pump outlet line 210 and the vent 158, while blocking communication with the main poεitive branch line 216. The pump 84 operateε to circulate air in a loop from the vent 158 through itε inlet and outlet lineε 208/210 back to the vent 158. b. The Pressure Actuating Network Aε Fig. 24 εhowε, the regulation system also includeε firεt and second presεure actuating networkε 230 and 232. The firεt preεεure actuating network 230 distributes negative and positive presεureε to the firεt pump actuator PAl and the valve actuatorε that εerve it (namely, VAl; VA2; VA8; VA9; and VA10). These actuators, in turn, operate casεette pump station PI and valve stations VI; V2; V8; V9; and V10, respectively, which εerve pump station PI. The second pressure actuating network 232 distributes negative and poεitive preεεures to the second pump actuator PA2 and the valve actuatorε that serve it (namely, VA3; VA4; VA5; VA6; and VA7). These actuators, in turn, operate cassette pump station P2 and casεette valve stations V3; V4; V5; V6; and V7, which serve pump station P2. The controller 16 can operate the first and second actuating networks 230 and 232 in tandem to alternately fill and empty the pump chambers PI and P2. This provides virtually continuous pumping action through the cassette 24 from the same source to the same destination. Alternatively, the controller 16 can operate the firεt and εecond actuating networkε 230 and 232 independently. In thiε way, the controller 16 can provide virtually εimultaneouε pumping action through the caεsette 24 between different sources and different destinationε. Thiε simultaneous pumping action can be conducted with either εynchronouε or non-εynchronouε preεsure delivery by the two networks 230 and 232. The networkε 230 and 232 can alεo be operated to provide preεεure delivery that driftε into an out of εynchronouεneεε. The firεt actuating network 230 provideε high- relative poεitive pressure and negative pressures to the valve actuators VAl; VA2; VA8; VA9; and VA10. The first actuating network 230 also selec- tively provides either high-relative poεitive and negative preεεure or low-relative poεitive and negative preεεure to the firεt pumping actuator PAl. Referring firεt to the valve actuators, three way valves CO; Cl; C2; C3; and C4 in the manifold assembly 162 control the flow of high-relative poεitive pressure and negative pressures to the valve actuatorε VAl; VA2; VA8; VA9; and VAIO. The high-relative poεitive preεsure region of the main branch line 216 communicates with the valveε CO; Cl: C2; C3; and C4 through a bridge line 234, a feeder line 236, and individual connecting lineε 238. The negative preεεure branch 212 communicateε with the valveε CO; Cl; C2; C3; and C4 through individual connecting lineε 340. The controller 16 εetε thiε branch 212 to a high-relative negative preεsure condition by εetting the tranεducer XNEG to εenεe a high-relative preεεure cut-off. By applying negative preεεure to one or more given valve actuatorε, the aεεociated caεεette valve etation iε opened to accommodate liquid flow. By applying poεitive preεεure to one or more given valve actuatorε, the aεεociated caεεette value εtation is closed to block liquid flow. In thiε way, the deεired liquid path leading to and from the pump chamber PI can be selected. Referring now to the pump actuator PAl, two way valve A4 in the manifold asεembly 162 communicateε with the high-relative preεεure feeder line 236 through connecting line 342. Two way valve A3 in the manifold aεεembly 162 communicateε with the low- relative poεitive preεεure reεervoir through connecting line 344. By selectively operating either valve A4 or A3, either high-relative or low- relative positive preεεure can be εupplied to the pump actuator PAl. Two way valve A0 communicateε with the negative preεεure branch 212 through connecting line 346. By setting the transducer XNEG to εenεe either a low- relative preεεure cut-off or a high-relative preεεure cut-off, either low-relative or high- relative preεεure can be εupplied to the pump actuator VAl by operation of valve AO. By applying negative preεεure (through valve AO) to the pump actuator PAl, the caεsette diaphragm 59 flexes out to draw liquid into the pump chamber PI. By applying positive presεure (through either valve A3 or A4) to the pump actuator PAl, the caεεette diaphragm 59 flexeε in to pump liquid from the pump chamber PI (provided, of course, that the associated inlet and outlet valves are opened) . By modulating the time period during which presεure iε applied, the pumping force can be modulated between full εtrokes and partial strokeε with reεpect to the pump chamber PI. The eecond actuating network 232 operateε like the firεt actuating network 230, except it serves the second pump actuator PA2 and its associated valve actuators VA3; VA4; VA5; VA6; and VA7. Like the first actuating network 230, the second actuating network 232 provides high-relative positive presεure and high-relative negative preεsures to the valve actuatorε VA3; VA4; VA5; VA6; and VA7. Three way valveε DI; D2: D3; D4; and D5 in the manifold aεεembly 162 control the flow of high- relative poεitive preεεure and high-relative negative pressureε to the valve actuatorε VA3; VA4; VA5; VA6; and VA7. The high-relative poεitive preεεure region 222 of the main branch line communicateε with the valveε DI; D2; D3; D4; and D5 through the bridge line 234, the feeder line 236, and connecting lines 238. The negative presεure branch 212 communicateε with the valveε DI: D2; D3; D4; and D5 through connecting lineε 340. Thiε branch 212 can be set to a high-relative negative pressure condition by setting the transducer XNEG to sense a high-relative presεure cut-off. Like the firεt actuating network 230, the second actuating network 232 selectively provides either high-relative poεitive and negative preεεure or low-relative poεitive and negative preεεure to the second pumping actuator PA2. Two way valve BO in the manifold asεembly 162 communicateε with the high-relative preεεure feeder line through connecting line 348. Two way valve station BI in the manifold asεembly 162 communicateε with the low- relative poεitive preεεure reεervoir through connecting line 349. By selectively operating either valve BO or BI, either high-relative or low- relative positive preεεure can be supplied to the pump actuator PA2. Two way valve B4 communicates with the negative preεεure branch through connecting line 350. By εetting the tranεducer XNEG to sense either a low- relative presεure cut-off or a high-relative preεεure cut-off, either low-relative or high- relative pressure can be supplied to the pump actuator PA2 by operation of valve B4. Like the first actuating network 230, by applying negative preεsure to one or more given valve actuators, the aεεociated caεεette value εtation iε opened to accommodate liquid flow. By applying positive presεure to one or more given valve actuatorε, the aεεociated caεεette value station is closed to block liquid flow. In thiε way, the deεired liquid path leading to and from the pump chamber P2 can be selected. By applying a negative preεεure (through valve B4) to the pump actuator PA2, the cassette diaphragm flexeε out to draw liquid into the pump chamber P2. By applying a poεitive preεεure (through either valve BBO or BI) to the pump actuator PA2, the caε¬ sette diaphragm flexes in to move liquid from the pump chamber P2 (provided, of courεe, that the associated inlet and outlet valves are opened) . By modulating the time period during which preεεure iε applied, the pumping force can be modulated between full strokes and partial strokeε with reεpect to the pump chamber P2. The firεt and second actuating networks 230/232 can operate in succession, one drawing liquid into pump chamber PI while the other pump chamber P2 pusheε liquid out of pump chamber P2, or vice verεa, to move liquid virtually continuouεly from the εame εource to the εame deεtination. The first and second actuating networks 230/232 can alεo operate to simultaneously move one liquid through pump chamber PI while moving another liquid through pump chamber P2. The pump chamberε PI and P2 and serve the same or different destinationε. Furthermore, with additional reεervoirs, the first and second actuation networks 232/232 can operate on the εame or different relative preεεure conditionε. The pump chamber PI can be operated with low-relative positive and negative pressure, while the other pump chamber P2 is operated with high-relative poεitive and negative preεεure. c. Liquid Volume Measurement As Fig. 24 shows, the presεure regulating εyεtem 200 alεo includeε a network 350 that works in conjunction with the controller 16 for measuring the liquid volumes pumped through the caεεette. The liquid volume meaεurement network 350 includes a reference chamber of known air volume (V.) associated with each actuating network. Reference chamber VSl is aεsociated with the firεt actuating network. Reference chamber VS2 iε aεεociated with the second actuating network. The reference chambers VSl and VS2 may be incorporated at part of the manifold asεembly 162, aε Fig. 20 εhowε. In a preferred arrangement (aε Fig. 14B shows) , the reference chamberε VSl and VS2 are carried by the piston element 102' itself, or at another located cloεe to the pump actuatorε PAl and PA2 within the caεεette holder 100. In thiε way, the reference chamberε VSl and VS2, like the pump actuatorε PAl and PA2, expoεed to generally the εame temperature conditionε aε the cassette itself. Also in the illustrated and preferred embodiment, insertε 117 occupy the reference chamberε VSl and VS2. Like the inεertε 117 carried within the pump actuatorε PAl and PA2, the reference chamber inεertε 117 are made of an open cell foam material. By dampening and directing the application of pneumatic preεεure, the reference chamber inεertε 117 make meaεurement of air volumes faster and lesε complicated. Preferably, the inεert 117 alεo includes a heat conducting coating or material to help conduct heat into the reference chamber VSl and VS2. In the illustrated embodiment, a thermal paεte iε applied to the foam inεert. Thiε preferred arrangement minimizeε the effectε of temperature differentialε upon liquid volume meaεurementε. Reference chamber VSl communicateε with the outlets of valves AO; A3: and A4 through a normally cloεed two way valve A2 in the manifold aεεembly 162. Reference chamber VSl alεo communicateε with a vent 352 through a normally cloεed two way valve Al in the manifold aεεembly 162. Tranεducer XVS1 in the manifold aεsembly 162 senseε the amount of air pressure preεent within the reference chamber VSl. Tranεducer XP1 senses the amount of air pressure present in the firεt pump actuator PAl. Likewise, reference chamber VS2 communicates with the outlets of valve BO; BI; and B4 through a normally closed two way valve B2 in the manifold aεεembly 162. Reference chamber VS2 also communicates with a filtered vent 356 through a normally closed two way valve B3 in the manifold assembly 162. Transducer XVS2 in the manifold assembly 162 senεeε the amount of air presεure preεent within the reference chamber VS2. Tranεducer XP2 senseε the amount of air preεεure preεent in the second pump actuator PA2. The controller 16 operates the network 350 to perform an air volume calculation twice, once during each draw (negative preεεure) cycle and once again during each pump (poεitive preεεure) cycle of each pump actuator PAl and PA2. The controller 16 operateε the network 350 to perform the first air volume calculation after the operating pump chamber is filled with the liquid to be pumped (i.e., after its draw cycle). This provides an initial air volume (V . The controller 16 operateε the network 350 to perform the second air volume calculation after moving fluid out of the pump chamber (i.e., after the pump cycle) . Thiε provideε a final air volume (V f ). The controller 16 calculates the difference between the initial air volume V L and the final air volume V f to derive a delivered liquid volume (V d ) , where: v d = v f - V, The controller 16 accumulates V d for each pump chamber to derive total liquid volume pumped during a given procedure. The controller 16 alεo applieε the incremental liquid volume pumped over time to derive flow rateε. The controller 16 deriveε V t in thiε way (pump chamber PI iε uεed aε an example) : (1) The controller 16 actuateε the valveε CO to C4 to cloεe the inlet and outlet paεεageε leading to the pump chamber PI (which iε filled with liquid) . Valves A2 and Al are normally closed, and they are kept that way. (2) The controller 16 opens valve Al to vent reference chamber VSl to atmoεphere. The controller 16 then conveyε poεitive pressure to the pump actuator PAl, by opening either valve A3 (low- reference) or A4 (high-reference) , depending upon the preεεure mode εelected for the pump stroke. (3) The controller 16 closes the vent valve Al and the poεitive preεεure valve A3 or A4, to iεolate the pump chamber PAl and the reference chamber VSl. (4) The controller 16 meaεureε the air preεεure in the pump actuator PAl (uεing tranεducer XP1) (IP dl ) and the air preεεure in the reference chamber VSl (uεing tranεducer XVS1) (IP #1 ) . (5) The controller 16 openε valve A2 to allow the reference chamber VSl to equilibrate with the pump chamber PAl. (6) The controller 16 meaεureε the new air preεsure in the pump actuator PAl (using transducer XPl) (IP^) and the new air presεure in the reference chamber (uεing tranεducer XVS1) (IP, 2 ) . (7) The controller 16 closes the poεitive preεεure valve A3 or A4. (8) The controller 16 calculateε initial air volume V 1 aε followε: V, - flP tl - IP, 2 ) * V_ (IP^ - IP dl ) After the pump chamber PI iε emptied of liquid, the same sequence of measurementε and calculations are made to derive V f , aε follows: (9) Keeping valve stationε A2 and Al cloεed, the controller 16 actuateε the valveε CO to C4 to cloεe the inlet and outlet passages leading to the pump chamber PI (which is now emptied of liquid) . (10) The controller 16 opens valve Al to vent reference chamber VSl to atmosphere, and then conveys poεitive preεεure to the pump actuator PAl, by opening either valve A3 (low-reference) or A4 (high-reference) , depending upon the preεsure mode εelected for the pump εtroke. (11) The controller 16 cloεeε the vent valve Al and the poεitive preεεure valve A3 or A4, to isolate the pump actuator PAl and the reference chamber VSl. (12) The controller 16 measures the air pressure in the pump actuator PAl (using transducer XPl) (FP dl ) and the air presεure in the reference chamber VSl (uεing tranεducer XVS1) (FP βl ) . (13) The controller 16 openε valve A2, allowing the reference chamber VSl to equilibrate with the pump actuator. (14) The controller 16 easureε the new air preεεure in the pump actuator PAl (using transducer XPl) (FP d2 ) and the new air preεεure in the reference chamber (uεing transducer XVS1) (FP, 2 ) . (15) The controller 16 closeε the poεitive preεεure valve A3 or A4. (16) The controller 16 calculateε final air volume V f aε followε: V f « C£P, ι - FP, 2 ) * V_ (FP d2 - FP dl ) The liquid volume delivered (V d ) during the preceding pump εtroke iε: d - V f - V, Preferably, before beginning another pump εtroke, the operative pump actuator iε vented to atmoεphere (by actuating valveε A2 and Al for pump actuator PAl, and by actuating valveε B2 and B3 for pump actuator PA2) . The controller 16 alεo monitorε the variation of V d over time to detect the preεence of air in the caεεette pump chamber P1/P2. Air occupying the pump chamber P1/P2 reduceε the capacity of the chamber to move liquid. If V d decreaεe over time, or if V d falls below a set expected value, the controller 16 attributes this condition to the buildup of air in the casεette chamber. When thiε condition occurε, the controller 16 conductε an air removal cycle, in which liquid flow through the affected chamber iε channeled through the top portion of the chamber to the drain or to the heater bag for a period of time. The air removal cycle ridε the chamber of exceεε air and reεtoreε V d to expected valueε. In another embodiment, the controller 16 periodically conducts an air detection cycle. In this cycle, the controller 16 delivers fluid into a given one of the pump chambers PI and P2. The controller 16 then cloεeε all valve stations leading into and out of the given pump chamber, to thereby trap the liquid within the pump chamber. The controller 16 then applies air presεure to the actuator associated with the pump chamber and deriveε a series of air volume V 1 measurementε over a period of time in the manner previously disclosed. Since the liquid trapped within the.pump chamber is relatively incompreεεible, there εhould be virtually no variation in the meaεured V t during the time period, unless there is air preεent in the pump chamber. If Vi doeε vary over a preεcribed amount during the time period, the controller 16 contributeε this to the presence of air in the pump chamber. When thiε condition occurε, the controller 16 conductε an air removal cycle in the manner previouεly deεcribed. The controller 16 performε the liquid volume calculations assuming that the temperature of the reference chamber VS1/VS2 does not differ significantly from the temperature of the pump chamber P1/P2. One way to minimize any temperature difference is to mount the reference chamber as close to the pump chamber as possible. Fig. 14B shows thiε preferred alternative, where the reference chamber iε phyεically mounted on the piεton head 116. Temperature differenceε can alεo be accounted for by applying a temperature correction factor (F t ) to the known air volume of the reference chamber V, to derive a temperature-corrected reference air volume V, t , aε followε: where: P t - £ t _ and where: C t iε the abεolute temperature of the cassette (expresεed in degreeε Rankine or Kelvin) , and R e iε the temperature of the reference chamber (expreεεed in the εame unitε aε C t ) . In thiε embodiment, the network εubεtituteε V M for V, in the above volume derivation calculationε. The value of F t can be computed baεed upon actual, real time temperature calculationε uεing temperature sensorε asεociated with the caεεette and the reference chamber. Because liquid volume measurementε are derived after each pumping εtroke, the same accuracy iε obtained for each caεεette loaded into the cycler, regardleεε of variationε in toleranceε that may exiεt among the caεsettes uεed. III. THE CYCLER CONTROLLER 16 Figε. 9; 10; 17; and 18 show the cycler controller 16. The controller 16 carries out proceεε control and monitoring functionε for the cycler 14. The controller 16 includeε a uεer interface 367 with a diεplay screen 370 and keypad 368. The user interface 367 receives characters from the keypad 368, diεplayε text to a diεplay screen 370, and sounds the speaker 372 (shown in Figs. 9 and 10) . The interface 367 preεentε status information to the uεer during a therapy session. The interface 367 also allows the user to enter and edit therapy parameters, and to iεsue therapy commands. In the illustrated embodiment, the controller 16 comprises a central microprocesεing unit (CPU) 358. The CPU is etched on the board 184 carried on stand off pins 182 atop the second module 88. Power harnesεeε 360 link the CPU 358 to the power supply 90 and to the operative elements of the manifold assembly 162. The CPU 358 employs conventional real-time multi-tasking to allocate CPU cycles to application taskε. A periodic timer interrupt (for example, every 10 milliεecondε) preemptε the executing taεk and schedules another that iε in a ready state for execution. If a reschedule iε requested, the highest priority task in the ready state is scheduled. Otherwise, the next taεk on the liεt in the ready εtate is scheduled. The following provides an overview of the operation of the cycler 14 under the direction of the controller CPU 358. (A) The user Interface 1. System Power UP/MAIN MENU (Fig. 25) When power is turned on, the controller 16 runs through an INITIALIZATION ROUTINE. During the initialization routine, the controller 16 verifieε that itε CPU 358 and aεεociated hardware are working. If theεe power-up teεtε fail, the controller 16 enterε a shutdown mode. If the power-up teεtε succeed, the controller 16 loads the therapy and cycle settingε saved in non-volatile RAM during the last power-down. The controller 16 runs a compariεon to determine whether theεe settings, as loaded, are corrupt. If the therapy and cycle εettings loaded from RAM are not corrupt, the controller 16 prompts the user to presε the GO key to begin a therapy seεsion. When the user presεeε the GO key, the controller 16 diεplays the MAIN MENU. The MAIN MENU allows the uεer to chooεe to (a) select the therapy and adjust the aεεociated cycle settings; (b) review the ultrafiltrate figures from the laεt therapy εeεεion, and (c) εtart the therapy session based upon the current εettingε. 2. THERAPY SELECTION MENU (Fig. 26. With choice (a) of the MAIN MENU selected, the controller 16 displayε the THERAPY SELECTION MENU. Thiε menu allowε the uεer to specify the APD modality desired, selecting from CCPD, IPD, and TPD (with an without full drain phaseε) . The uεer can alεo select an ADJUST CYCLE SUBMENU. This submenu allows the user to select and change the therapy parameters. For CCPD and IPD modalities, the therapy parameterε include the THERAPY VOLUME, which iε the total dialyεate volume to be infuεed during the therapy εeεεion (in ml) ; the THERAPY TIME, which iε the total time allotted for the therapy (in hourε and minuteε) ; the FILL VOLUME, which iε the volume to be infuεed during each fill phaεe (in ml) , baεed upon the size of the patient's peritoneal cavity; the LAST FILL VOLUME, which iε the final volume to be left in the patient at the end of the εession (in ml) ; and SAME DEXTROSE (Y OR N) , which allows the uεer to εpecify a different dextroεe concentration for the laεt fill volume. -.-, - 57 - For the TPD modality, the therapy parameterε include THERAPY VOLUME, THERAPY TIME, LAST FILL VOLUME, AND SAME DEXTROSE (Y OR N) , as above described. In TPD, the FILL VOLUME parameter is the initial tidal fill volume (in ml) . TPD includes also includes as additional parameters TIDAL VOLUME PERCENTAGE, which iε the fill volume to be infused and drained periodically, expressed as a percentage of the total therapy volume; TIDAL FULL DRAINS, which iε the number of full drainε in the therapy εeεεion; and TOTAL UF, which is the total ultrafiltrate expected from the patient during the seεsion (in ml) , based upon prior patient monitoring. The controller 16 includes a THERAPY LIMIT TABLE. This Table setε predetermined maximum and minimum limite and permitted incrementε for the therapy parameterε in the ADJUST CYCLE SUBMENU. The controller 16 alεo includeε a THERAPY VALUE VERIFICATION ROUTINE. This routine checks the parameters selected to verify that a reasonable therapy sesεion haε been programmed. The THERAPY VALUE VERIFICATION ROUTINE checkε to aεεure that the εelected therapy parameterε include a dwell time of at leaεt one minute; at leaεt one cycle; and for TPD the expected filtrate iε not unreasonably large (i.e., it is lesε than 25% of the selected THERAPY VOLUME) . If any of these parameters iε unreaεonable, the THERAPY VALUE VERIFICATION ROUTINE placeε the uεer back in the ADJUST CYCLE SUBMENU and identifieε the therapy parameter that iε oεt likely to be wrong. The uεer iε required to program a reasonable therapy before leaving the ADJUST CYCLE SUBMENU and begin a therapy εeεεion. Once the modality iε selected and verified, the controller 16 returnε to uεer to the MAIN MENU. 3. REVIEW ULTRAFILTRATION MENU With choice (b) of the MAIN MENU selected, the controller 16 displays the REVIEW ULTRAFILTRATION MENU (see Fig. 25) . This Menu dieplayε LAST UF, which iε the total volume of ultrafiltrate generated by the perviouε therapy sesεion. For CCPD and IPD modalitieε, the uεer can alεo select to ULTRAFILTRATION REPORT. This Report provides a cycle by cycle breakdown of the ultrafiltrate obtained from the previouε therapy εeεεion. 4. SET-UP PROMPTS/LEAK TESTING With choice (c) of the MAIN MENU εelected, the controller 16 firεt diεplayε SET-UP PROMPTS to the uεer (aε shown in Fig. 27) . The SET-UP PROMPTS firεt inεtruct the uεer to LOAD SET. The uεer iε required to open the door; load a caεεette; cloεe the door; and press GO to continue with the set-up dialogue. When the user preεεeε GO, the controller 16 preεεurizeε the main bladder and occluder bladder and teεtε the door εeal. If the door seal fails, the controller 16 promptε the uεer to try again. If the door continues to fail a predetermined period of timeε, the controller 16 raiεeε a SYSTEM ERROR and εhutε down. If the door eeal iε made, the SET-UP PROMPTS next inεtruct the uεer to CONNECT BAGS. The user iε required to connect the bagε required for the therapy εeεεion; to unclamp the liquid tubing lineε being uεe and aεεure that the liquid lineε that are not remained clamped (for example, the selected therapy may not require final fill bags, so liquid lines to these bags should remain clamped) . Once the user accomplishes these taskε, he/she presses GO to continue with the set-up dialogue. When GO is pressed, the controller 16 checks which lines are clamped and uεeε the programmed therapy parameterε to determine which lineε should be primed. The controller 16 primes the appropriate lineε. Priming removeε air from the set lines by delivering air and liquid from each bag used to the drain. Next, the controller 16 performs a predetermined series of integrity testε to aεεure that no valveε in the caεεette leak; that there are no leakε between pump chamberε; and that the occluder aεεembly stops all liquid flow. The integrity testε first convey the predetermined high-relative negative air pressure (- 5.0 pεig) to the valve actuatorε VAl to VAIO. The transducer XNEG monitors the change in high-relative negative air preεεure for a predetermined period. If the preεsure change over the period exceedε a predetermined maximum, the controller 16 raises a SYSTEM ERROR and εhutε down. Otherwise, the integrity testε convey the predetermined high-relative poεitive preεsure (7.0 psig) to the valve actuatore VAl to VAIO. The transducer XHPOS monitors the change in high- relative positive air presεure for a predetermined period. If the preεεure change over the period exceedε a predetermined maximum, the controller 16 raiεes a SYSTEM ERROR and shuts down. Otherwise, the integrity testε proceed. The valve actuatorε VAl to VA10 convey poεitive preεεure to close the casεette valve stations VI to VIO. The testε first convey the predetermined maximum high- relative negative pressure to pump actuator PAl, while conveying the predetermined maximum high- relative positive presεure to pump actuator PA2. The tranεducerε XPl and XP2 monitor the pressures in the respective pump actuatorε PAl and PA2 for a predetermined period. If preεεure changes over the period exceed a predetermined maximum, the controller 16 raiseε a SYSTEM ERROR and εhutε down. Otherwise, the testε next convey the predetermined maximum high-relative poεitive preεεure to pump actuator PAl, while conveying the predetermined maximum high-relative negative preεεure to pump actuator PA2. The tranεducerε XPl and XP2 monitor the preεεureε in the reεpective pump actuatorε PAl and PA2 for a predetermined period. If preεεure changeε over the period exceed a predetermined maximum, the controller 16 raises a SYSTEM ERROR and shuts down. Otherwise, power to valve C6 is interrupted. This ventε the occluder bladder 152 and urgeε the occluder blade and plate 144/148 together, crimping caεεette tubing 26 to 34 cloεed. The pump chamberε PI and P2 are operated at the predetermined maximum pressure conditions and liquid volume meaεurementε taken in the manner previouεly deεcribed. If either pump chamber P1/P2 moves liquid pasε the cloεed occluder blade and plate 144/148, the controller 16 raises a SYSTEM ERROR and shuts down. If all integrity testε succeed, the SET-UP PROMPTS next instruct the user to CONNECT PATIENT. The user is required to connect the patient according to the operator manual and presε GO to begin the dialyεiε therapy εeεεion εelected. The controller 16 beginε the sesεion and displays the RUN TIME MENU. 5. RUN TIME MENU Attention is now directed to Fig. 28. The RUN TIME MENU is the active therapy interface. The RUN TIME MENU provides an updated real-time status report of the current progress of the therapy sesεion. The RUN TIME MENU includeε the CYCLE STATUS, which identifies the total number of fill/dwell/drain phases to be conducted and the present number of the phase underway (e.g., Fill 3 of 10) ; the PHASE STATUS, which displayε the present fill volume, counting up from 0 ml; the ULTRAFILTRATION STATUS, which displays total ultrafiltrate accumulated since the start of the therapy sesεion; the TIME, which iε the preεent time; and FINISH TIME, which ie the time that the therapy sesεion iε expected to end. Preferably, the uεer can also select in the RUN TIME MENU an ULTRAFILTRATION STATUS REVIEW SUBMENU, which displayε a cycle by cycle breakdown of ultrafiltration accumulated. From the RUN TIME MENU, the user can also εelect to STOP. The controller 16 interruptε the therapy session and displays the STOP SUBMENU. The STOP SUBMENU allows the user to REVIEW the programmed therapy parameters and make change to the parameterε; to END the therapy session; to CONTINUE the therapy sesεion; to BYPASS the preεent phaεe; to conduct a MANUAL DRAIN; or ADJUST the intenεity of the display and loudnesε of alarmε. REVIEW reεtrictε the type of changeε that the uεer can make to the programmed parameters. For example, in REVIEW, the user cannot adjust parameters above or below a maximum specified amounts. CONTINUE returns the user to the RUN TIME MENU and continue the therapy sesεion where it left off. The controller 16 preferably alεo includeε specified time-outs for the STOP SUBMENU. For example, if the uεer doeε not take any action in the STOP SUBMENU for 30 inuteε, the controller 16 automatically executeε CONTINUE to return to the RUN TIME MENU and continue the therapy eeεεion. If the uεer doeε not take any action for 2 minuteε after εelecting REVIEW, the controller 16 also automatically executes CONTINUE. 6. Background Monitoring Routine/System Errors The controller 16 includes a BACKGROUND MONITORING ROUTINE that verifieε εyεtem integrity at a predetermined intervals during the therapy sesεion (e.g., every 10 seconds) (as Fig. 29 εhowε). The BACKGROUND MONITORING ROUTINE includeε BAG OVER TEMP, which verifieε that the heater bag iε not too hot (e.g., not over 44 degreeε C) ; DELIVERY UNDER TEMP, which verifieε that the liquid delivered to the patient iε not too cold (e.g, leεε than 33 degrees C) ; DELIVERY OVER TEMP, which verifies that the liquid delivered to the patient iε not too hot (e.g, over 38 degreeε C) ; MONITOR TANKS, which verifieε that the air tankε are at their operating preεεureε (e.g., poεitive tank preεεure at 7.5 pεi +/" 0.7 pεi; patient tank at 5.0 pεi +/- 0.7 psi, except for heater to patient line, which iε 1.5 pεi +/" °« 2 pεi; negative tank preεεure at -5.0 pεi +/" 0.7pεi, except for patient to drain line, which is at -0.8 psi +/- 0.2 psi) ; CHECK VOLTAGES, which verify that power supplies are within their noise and tolerance specs; VOLUME CALC, which verifies the volume calculation math; and CHECK CPU, checks the procesεor and RAM. When the BACKGROUND MONITORING ROUTINE senses an error, the controller 16 raises a SYSTEM ERROR. Loss of power also raiseε a SYSTEM ERROR. When SYSTEM ERROR occurε, the controller 16 εoundε an audible alarm and diεplayε a meεεage informing the uεer about the problem sensed. When SYSTEM ERROR occurs, the controller 16 also shuts down the cycler 14. During shut down, the controller 16 ensureε that all liquid delivery is stopped, activates the occluder asεembly, closes all liquid and air valves, turnε the heater plate elements off. If SYSTEM ERROR occurs due to power failure, the controller 16 alεo ventε the emergency bladder, releaεing the door. 7 . SELF-DIAGNOSTICS AND TROUBLE SHOOTING According to the invention, the controller 16 monitorε and controlε pneumatic preεsure within the internal presεure distribution system 86. Based upon pneumatic presεure meaεurementε, the controller 16 calculates the amount and flow rate of liquid moved. The controller doeε not require an additional external sensing devices to perform any of itε control or measurement functions. As a result, the system 10 requires no external pressure, weight, or flow sensorε for the tubing 26 to 34 or the bags 20/22 to monitor and diagnoεe liquid flow conditionε. The eame air preεεure that moveε liquid through the system 10 also serves to sense and diagnose all relevant external conditions affecting liquid flow, like an empty bag condition, a full bag condition, and an occluded line condition. Moreover, strictly by monitoring the pneumatic presεure, the controller 16 iε able to distinguish a flow problem emanating from a liquid source from a flow problem emanating from a liquid destination. Based upon the liquid volume measurementε derived by the meaεurement network 350, the controller 16 alεo deriveε liquid flow rate. Baεed upon valueε and changeε in derived liquid flow rate, the controller 16 can detect an occluded liquid flow condition. Furthermore, baεed upon derived liquid flow rates, the controller can diagnose and determine the cause of the occluded liquid flow condition. The definition of an "occluded flow" condition can vary depending upon the APD phase being performed. For example, in a fill phase, an occluded flow condition can represent a flow rate of leεε than 20 ml/min. In a drain phaεe, the occluded flow condition can repreεent a flow rate of less than 10 ml/min. In a bag to bag liquid transfer operation, an occluded flow condition can represent a flow rate of lesε than 25 ml/min. Occluded flow conditionε for pediatric APD sessions can be placed at lower set points. When the controller 16 detectε an occluded flow condition, it implementε the following heuristic to determine whether the occlusion iε attributable to a given liquid source or a given liquid destination. When the controller 16 determines that the cassette cannot draw liquid from a given liquid source above the occluded flow rate, the controller 16 determines whether the caεεette can move liquid toward the source above the occluded flow rate (i.e., it determines whether the liquid source can serve as a liquid destination) . If it can, the controller 16 diagnoseε the condition aε an empty liquid source condition. When the controller 16 determines that the cassette cannot push liquid toward a given destination above the occluded flow rate, it determines whether the caεεette can draw liquid from the destination above the occluded flow rate (i.e., it determineε whether the liquid deεtination can εerve aε a liquid source) . If it can, the controller diagnoseε the condition aε being a full liquid deεtination condition. When the controller 16 determineε that the caεεette can neither draw or puεh liquid to or from a given source or destination above the occluded flow rate, the controller 16 interprets the condition aε an occluded line between the cassette and the particular source or destination. In thiε way, the εyεtem 10 operateε by controlling pneumatic fluid pressure, but not by reacting to external fluid or liquid presεure or flow sensing. 8. ALARMS With no SYSTEM ERRORS, the therapy sesεion automatically continues unless the controller 16 raiεeε an ALARM1 or ALARM2. Fig. 30 shows the ALARM1 and ALARM2 routines. The controller 16 raises ALARM1 in situations that require user intervention to correct. The controller 16 raiseε ALARM1 when the controller 16 εenεeε no supply liquid; or when the cycler 14 iε not level. When ALARM1 occurε, the controller 16 suspendε the therapy εeεεion and εoundε an audible alarm. The controller 16 alεo displays an ALARM MENU that informs the user about the condition that should be corrected. The ALARM MENU gives the uεer the choice to correct the condition and CONTINUE; to END the therapy; or to BYPASS (i.e., ignore) the condition and resume the therapy εeεsion. The controller 16 raiseε ALARM2 in εituationε that are anomalieε but will typically correct themεelveε with minimum or no uεer intervention. For example, the controller 16 raiεeε ALARM2 when the controller 16 initially εenεeε a low flow or an occluded lineε. In thiε situation, the patient might have rolled over onto the catheter and may need only to move to rectify the matter. When ALARM2 occurs, the controller 16 generates a first audible signal (e.g., 3 beeps). The controller 16 then mutes the audible signal for 30 εecondε. If the condition εtill exiεtε after 30 second, the controller 16 generates a second audible εignal (e.g., 8 beepε) The controller 16 again muteε the audible εignal. If the condition εtill exiεts 30 secondε later, the controller 16 raiεeε an ALARM1, aε deεcribed above. The uεer iε then required to intervene uεing the ALARM MENU. 9. POST THERAPY PROMPTS The controller 16 terminates the sesεion when (a) the preεcribed therapy sesεion iε εucceεεfully completed; (b) the uεer εelectε END in the STOP SUBMENU or the ALARM MENU; or (c) a SYSTEM ERROR condition occurε (εee Fig. 31) . When any of theεe eventε occur, the controller 16 diεplays POST THERAPY PROMPTS to the user. The POST THERAPY PROMPTS inform the user THERAPY FINISHED, to CLOSE CLAMPS, and to DISCONNECT PATIENT. The user presεeε GO to advance the promptε. Once the uεer diεconnectε the patient and presses GO, the controller 16 displayε PLEASE WAIT and depreεsurizes the door. Then the controller 16 then directε the uεer to REMOVE SET. Once the uεer removes the set and presεeε GO, the controller 16 returnε to uεer to the MAIN MENU. (B) Controlling an APD Therapy Cycle 1. Fill Phase In the fill phaεe of a typical three phaεe APD cycle, the cycler 14 tranεfere warmed dialysate from the heater bag 22 to the patient. The heater bag 22 is attached to the first (uppermost) casεette port 27. The patient line 34 iε attached to the fifth (bottommost) cassette port 35. As Fig. 32 shows, the fill phase involves drawing warmed dialysate into cassette pump chamber PI through primary liquid path Fl via branch liquid path F6. Then, pump chamber PI expels the heated dialysate through primary liquid path F5 via branch liquid path F8. To expedite pumping operationε, the controller 16 preferably workε pump chamber P2 in tandem with pump chamber PI. The controller 16 drawε heated dialyεate into pump chamber P2 through primary liquid path Fl via branch liquid path F7. Then, pump chamber P2 expels the heated dialyεate through primary liquid path F5 through branch liquid path F9. The controller 16 workε pump chamber PI in a draw stroke, while working pump chamber P2 in a pump stroke, and vice versa. In this sequence, heated dialyεate iε alwayε introduced into the top portions of pump chamberε PI and P2. The heated dialyεate iε alwayε diεcharged through the bottom portionε of pump chamberε PI and P2 to the patient free of air. Furthermore, during liquid tranεfer directly with the patient, the controller 16 can supply only low-relative poεitive and negative preεεureε to the pump actuatorε PAl and PA2. In carrying out thiε taεk, the controller 16 alternateε the following sequences 1 and 2: 1. Perform pump chamber PI draw stroke (drawing a volume of heated dialysate into pump chamber PI from the heater bag) , while performing pump chamber P2 pump εtroke (expelling a volume of heated dialyεate from pump chamber P2 to the patient) . (i) Open inlet path Fl to pump chamber PI, while cloεing inlet path Fl to pump chamber P2. Actuate valve CO to supply high-relative negative presεure to valve actuator VAl, opening caεsette valve station VI. Actuate valves Cl; DI; and D2 to εupply high-relative poεitive preεsure to valve actuatorε VA2; VA3: and VA4, cloεing caεεette valve εtation V2; V3; and V4. (ii) Cloεe outlet path F5 to pump chamber PI, while opening outlet path F5 to pump chamber P2. Actuate valveε C2 to C4 and D3 to D5 to εupply high-relative poεitive preεεure to valve actuatorε VA8 to VIO and VA5 to VA7, cloεing caεsette valve stations V8 to VIO and V5 to V7. Actuate valve D5 to supply high-relative negative pressure to valve actuator VA7, opening cassette valve station V7. (iii) Flex the diaphragm underlying actuator PAl out. Actuate valve AO to supply low- relative negative pressure to pump actuator PAl. (iv) Flex the diaphragm underlying actuator PA2 in. Actuate valve BI to supply low- relative positive pressure to pump actuator PA2. 2. Perform pump chamber P2 draw stroke (drawing a volume of heated dialysate into pump chamber P2 from the heater bag) , while performing pump chamber PI pump stroke (expelling a volume of heated dialysate from pump chamber PI to the patient) . (i) Open inlet path Fl to pump chamber P2, while closing inlet path Fl to pump chamber PI. Actuate valves CO; Cl; and D2 to supply high- relative positive preεεure to valve actuatorε VAl; VA2; and VA4, cloεing caεsette valve stations VI; V2; and V4. Actuate valve DI to supply high- relative negative presεure to valve actuator VA3, opening caεεette valve εtation V3. (ii) Cloεe outlet path F5 to pump chamber P2, while opening outlet path F5 to pump chamber PI. Actuate valve C2 to supply high-relative negative pressure to valve actuator VA8, opening casεette valve station V8. Actuate valves D3 to D5; C2; and C4 to supply high-relative positive preεsure to valve actuatorε VA5 to VA7; V9; and VIO, cloεing cassette valve stations V5 to V7; V9; and VIO. (iii) Flex the diaphragm underlying actuator PAl in. Actuate valve A3 to supply low- relative positive presεure to pump actuator PAl. (iv) Flex the diaphragm underlying actuator PA2 out. Actuate valve B4 to supply low- relative negative presεure to pump actuator PA2. 2. Dwell Phase Once the programmed fill volume haε been tranεferred to the patient, the cycler 14 enterε the second or dwell phase. In this phaεe, the cycler 14 repleniεheε the heater bag by supplying fresh dialyεate from a source bag. The heater bag . is attached to the first (uppermost) casεette port. The εource bag line iε attached to the fourth caεεette port, immediately above the patient line. Aε Fig. 33 εhowε, the repleniεh heater bag phaεe involveε drawing freεh dialyεate into cassette pump chamber PI through primary liquid path F4 via branch liquid path F8. Then, pump chamber PI expels the dialyεate through primary liquid path Fl via branch liquid path F6. To expedite pumping operationε, the controller 16 preferably workε pump chamber P2 in tandem with pump chamber PI. The controller 16 drawε fresh dialysate into cassette pump chamber P2 through primary liquid path F4 via branch liquid path F9. Then, pump chamber P2 expels the dialysate through primary liquid path Fl via branch liquid path F7. The controller 16 workε pump chamber PI in a draw stroke, while working pump chamber P2 in a pump εtroke, and vice versa. In this sequence, fresh dialyεate is alwayε introduced into the bottom portionε of pump chamberε PI and P2. The freεh dialyεate iε alwayε discharged through the top portions of pump chamberε PI and P2 to the heater bag. Thiε allowε entrapped air to be removed from the pump chamberε PI and P2. Furthermore, since liquid transfer doeε not occur directly with the patient, the controller 16 supplies high-relative positive and negative pressureε to the pump actuatorε PAl and PA2. In carrying out thiε taεk, the controller 16 alternateε the following sequences: 1. Perform pump chamber PI draw stroke (drawing a volume of fresh dialysate into pump chamber PI from a source bag) , while performing pump chamber P2 pump stroke (expelling a volume of fresh dialysate from pump chamber P2 to the heater bag) . (i) Open inlet path F4 to pump chamber PI, while closing inlet path F4 to pump chamber P2. Actuate valve C3 to supply high-relative negative preεεure to valve actuator VA9, opening cassette valve station V9. Actuate valves D3 to D5; C2; and C4 to supply high-relative positive pressure to valve actuatorε VA5 to VA8; and VAIO, cloεing caεεette valve εtationε V5 to V8 and VIO. (ii) Cloεe outlet path Fl to pump chamber PI, while opening outlet path Fl to pump chamber P2. Actuate valveε CO; Cl; and D2 to supply high- relative positive pressure to valve actuators VAl; VA2 and VA4, cloεing caεεette valve stations VI; V2; and V4. Actuate valve DI to supply high-relative negative presεure to valve actuator VA3, opening caεεette valve station V3. (iii) Flex the diaphragm underlying actuator PAl out. Actuate valve AO to supply high- relative negative pressure to pump actuator PAl. (iv) Flex the diaphragm underlying actuator PA2 in. Actuate valve BO to supply high- relative poεitive preεεure to pump actuator PA2. 2. Perform pump chamber P2 draw stroke (drawing a volume of fresh dialyeate into pump chamber P2 from a source bag) , while performing pump chamber PI pump stroke (expelling a volume of fresh dialysate from pump chamber PI to heater bag) . (i) Close inlet path F4 to pump chamber PI, while opening inlet path F4 to pump chamber P2. Actuate valve D5 to supply high-relative negative presεure to valve actuator VA6, opening caεεette valve station V6. Actuate valves C3 to C4; D3; and D5 to supply high-relative positive pressure to valve actuators VA5 and VA7 to VAIO, closing casεette valve stations V5 and V7 to VIO. (ii) Open outlet path Fl to pump chamber PI, while closing outlet path Fl to pump chamber P2. Actuate valve CO to εupply high-relative negative presεure to valve actuator VAl, opening caεεette valve station VI. Actuate valves Cl; DI; and D2 to εupply high-relative poεitive preεεure to valve actuatore VA2 to VA4, cloεing caεεette valve station V2 to V4. (iii) Flex the diaphragm underlying actuator PAl in. Actuate valve A4 to supply high- relative positive pressure to pump actuator PAl. (iv) Flex the diaphragm underlying actuator PA2 out. Actuate valve B4 to supply high- relative negative presεure to pump actuator PA2. 3. Drain Phase When the programmed drain phaεe endε, the cycler 14 enterε the third or drain phaεe. In thiε phaεe, the cycler 14 tranεferε epent dialyεate from the patient to a drain. The drain line iε attached to the second caεεette port. The patient line iε attached to the fifth, bottommost cassette port. As Fig. 34 shows, the drain phase involveε drawing spent dialysate into casεette pump chamber PI through primary liquid path F5 via branch liquid path F8. Then, pump chamber PI expelε the dialysate through primary liquid path F2 via branch liquid path F6. To expedite pumping operations, the controller 16 works pump chamber P2 in tandem with pump chamber PI. The controller 16 draws spend dialysate into casεette pump chamber P2 through primary liquid path F5 via branch liquid path F9. Then, pump chamber P2 expelε the dialyεate through primary liquid path F2 via branch liquid path F7. The controller 16 workε pump chamber PI in a draw stroke, while working pump chamber P2 in a pump εtroke, and vice versa. In this sequence, spent dialysate is always introduced into the bottom portions of pump chamberε PI and P2. The spent dialysate is always discharged through the top portions of pump chamberε PI and P2 to the heater bag. Thiε allowε air to be removed from the pump chamberε PI and P2. Furthermore, εince liquid tranεfer doeε occur directly with the patient, the controller 16 εupplies low-relative positive and negative presεureε to the pump actuatorε PAl and PA2. In carrying out thiε task, the controller 16 alternates the following sequences: 1. Perform pump chamber PI draw stroke (drawing a volume of spent dialysate into pump chamber PI from the patient) , while performing pump chamber P2 pump stroke (expelling a volume of spent dialysate from pump chamber P2 to the drain) . (i) Open inlet path F5 to pump chamber PI, while cloεing inlet path F5 to pump chamber P2. Actuate valve C2 to supply high-relative negative presεure to valve actuator VA8, opening cassette valve station V8. Actuate valves D3 to D5, C3, and C4 to supply high-relative positive preεεure to valve actuatorε VA5 to VA7, VA9 and VAIO, closing cassette valve stations V5 to V7, V9, and VIO. (ii) Close outlet path F2 to pump chamber PI, while opening outlet path F2 to pump chamber P2. Actuate valveε CO; Cl; and DI to εupply high- relative poεitive preεεure to valve actuatorε VAl; VA2 and VA3, cloεing caεεette valve εtationε VI; V2; and V3. Actuate valve D2 to εupply high-relative negative preεεure to valve actuator VA4, opening caεεette valve εtation V4. (iii) Flex the diaphragm underlying actuator PAl out. Actuate valve AO to supply low- relative negative presεure to pump actuator PAl. (iv) Flex the diaphragm underlying actuator PA2 in. Actuate valve BI to εupply low- relative poεitive preεεure to pump actuator PA2. 2. Perform pump chamber P2 draw stroke (drawing a volume of spent dialysate into pump chamber P2 from the patient) , while performing pump chamber PI pump εtroke (expelling a volume of εpent dialyεate from pump chamber PI to the drain) . (i) Cloεe inlet path F5 to pump chamber PI, while opening inlet path F5 to pump chamber P2. Actuate valve D5 to εupply high-relative negative preεεure to valve actuator VA7, opening caεεette valve station V7. Actuate valves D3; D4 and C2 to C4 to supply high-relative poεitive preεsure to valve actuators VA5; VA6; and VA8 to VAIO, cloεing caεεette valve etationε V5, V6, and V8 to VIO. (ii) Open outlet path F2 to pump chamber PI, while cloεing outlet path F2 to pump chamber P2. Actuate valve Cl to supply high-relative negative presεure to valve actuator VA2, opening cassette valve station V2. Actuate valves CO; DI; and D2 to supply high-relative positive presεure to valve actuators VAl; VA3; and VA4, closing cassette valve station VI; V3; and V4. (iii) Flex the diaphragm underlying actuator PAl in. Actuate valve A3 to supply low- relative positive presεure to pump actuator PAl. (iv) Flex the diaphragm underlying actuator PA2 out. Actuate valve B4 to supply low- relative negative pressure to pump actuator PA2. The controller 16 senseε preεεure uεing tranεducerε XPl and XP2 to determine when the patient'ε peritoneal cavity iε empty. The drain phase is followed by another fill phaεe and dwell phaεe, aε previouεly deεcribed. 4. Last Dwell Phase In some APD procedures, like CCPD, after the last prescribed fill/dwell/drain cycle, the cycler 14 infuseε a final fill volume. The final fill volume dwellε in the patient through the day. It iε drained at the outεet of the next CCPD sesεion in the evening. The final fill volume can contain a different concentration of dextroεe than the fill volume of the succesεive CCPD fill/dwell/drain fill cycleε the cycler 14 provideε. The choεen dextrose concentration sustainε ultrafiltration during the day-long dwell cycle. In thiε phase, the cycler 14 infuseε freεh dialyεate to the patient from a "laεt fill" bag. The "laεt fill" bag iε attached to the third caεεette port. During the laεt εwell phaεe, the heater bag iε emptied, and solution from last bag volume is transferred to the heater bag. From there, the last fill solution is transferred to the patient to complete the last fill phase. The last dwell phaεe involveε drawing liquid from the heater bag into pump chamber PI through primary liquid path Fl via branch path F6. The, the pump chamber PI expelε the liquid to the drain through primary liquid path F2 via branch liquid path F6. To expedite drainage of the heater bag, the controller 16 workε pump chamber P2 in tandem with pump chamber PI. The controller 16 draws liquid from the heater bag into pump chamber P2 through primary liquid path Fl via branch liquid path F7. Then, pump chamber P2 expels liquid to the drain through primary liquid path F2 via branch liquid path F7. The controller 16 works pump chamber PI in a draw stroke, while working pump chamber P2 in a pump εtroke, and vice verεa. Once the heater bag iε drained, the controller 16 drawε freεh dialyεate from the "laεt fill" bag into caεsette pump chamber PI through primary liquid path F3 via branch liquid path F8. Then, pump chamber PI expels the dialyεate to the heater bag through primary liquid path Fl via the branch liquid path F6. Aε before, to expedite pumping operations, the controller 16 preferably workε pump chamber P2 in tandem with pump chamber PI. The controller 16 drawε freεh dialyεate from the "laεt fill" bag into caεεette pump chamber P2 through primary liquid path F3 via branch liquid path F9. Then, pump chamber P2 expelε the dialyεate through primary liquid path Fl via the branch liquid path F7. The controller 16 workε pump chamber PI in a draw εtroke, while working pump chamber P2 in a pump stroke, and vice versa. In this sequence, fresh dialysate from the "last fill" bag is alwayε introduced into the bottom portionε of pump chamberε PI and P2. The freεh dialyεate is alwayε diεcharged through the top portionε of pump chamberε PI and P2 to the heater bag. Thiε allowε air to be removed from the pump chambers Pi and P2. Furthermore, since liquid transfer doeε not occur directly with the patient, the controller 16 can supply high-relative positive and negative preεεureε to the pump actuatorε PAl and PA2. In carrying out thiε taεk, the controller 16 alternateε the following εequenceε (see Fig. 35) : 1. Perform pump chamber PI draw stroke (drawing a volume of fresh dialyεate into pump chamber PI from the "last fill" bag) , while performing pump chamber P2 pump εtroke (expelling a volume of freεh dialyεate from pump chamber P2 to the heater bag) . (i) Open inlet path F3 to pump chamber PI, while cloεing inlet path F3 to pump chamber P2. Actuate valve C4 to supply high-relative negative pressure to valve actuator VAIO, opening casεette valve εtation VIO. Actuate valveε D3 to D5; C2; and C3 to supply high-relative positive presεure to valve actuators VA5 to VA9, closing caεεette valve εtationε V5 to V9. (ii) Cloεe outlet path Fl to pump chamber PI, while opening outlet path Fl to pump chamber P2. Actuate valveε CO; Cl; and D2 to εupply high- relative positive preεεure to valve actuatorε VAl; VA2 and VA4, closing casεette valve stations VI; V2; and V4. Actuate valve DI to supply high-relative negative presεure to valve actuator VA3, opening caεεette valve station V3. (iii) Flex the diaphragm underlying actuator PAl out. Actuate valve AO to supply high- relative negative presεure to pump actuator PAl. (iv) Flex the diaphragm underlying actuator PA2 in. Actuate valve BO to supply high- relative positive preεεure to pump actuator PA2. 2. Perform pump chamber P2 draw stroke (drawing a volume of fresh dialysate into pump chamber P2 from the "laεt fill" bag) , while performing pump chamber PI pump εtroke (expelling a volume of freεh dialyεate from pump chamber PI to heater bag) . (i) Cloεe inlet path F3 to pump chamber PI, while opening inlet path F3 to pump chamber P2. Actuate valve D3 to supply high-relative negative presεure to valve actuator VA5, opening caεεette valve station V5. Actuate valves C2 to C4; D4; and D5 to supply high-relative positive preεεure to valve actuatorε VA6 to VAIO, cloεing caεεette valve εtationε V6 to VIO. (ii) Open outlet path Fl to pump chamber PI, while cloεing outlet path Fl to pump chamber P2. Actuate valve CO to eupply high-relative negative preεεure to valve actuator VAl, opening caεεette valve εtation VI. Actuate valveε Cl; DI; and D2 to εupply high-relative poεitive preεεure to valve actuatorε VA2 to VA4, cloεing caεεette valve εtation V2 to V4. (iii) Flex the diaphragm underlying actuator PAl in. Actuate valve A4 to supply high- relative positive presεure to pump actuator PAl. (iv) Flex the diaphragm underlying actuator PA2 out. Actuate valve B4 to supply high- relative negative presεure to pump actuator PA2. Once the laεt fill solution has been heated, it is tranεferred to the patient in a fill cycle aε described above (and as Fig. 32 shows) . According to one aspect of the invention, every important aspect of the APD procedure iε controlled by fluid pressure. Fluid presεure moveε liquid through the delivery set, emulating gravity flow conditions based upon either fixed or variable headheight conditions. Fluid presεure controlε the operation of the valveε that direct liquid among the multiple deεtinationε and εourceε. Fluid preεεure serves to seal the casεette within the actuator and provide a failεafe occlusion of the associated tubing when conditionε warrant. Fluid preεεure iε the baεiε from which delivered liquid volume meaεurementε are made, from which air entrapped in the liquid is detected and elimination, and from which occluded liquid flow conditions are detected and diagnosed. According to another aspect of the invention, the caεεette serves to organize and mainfold the multiple lengths of tubing and bagε that peritoneal dialyεiε requires. The casεette alεo serves to centralize all pumping and valving activities required in an automated peritoneal dialysis procedure, while at the same time serving as an effective sterility barrier. Various featureε of the invention are εet forth in the following claimε.

Claims: I Claim: 1. A peritoneal dialysiε εyεtem compriεing a liquid distribution casεette including a pumping echaniεm compriεing a diaphragm aεεociated with the pump chamber, and meanε for eεtabliεhing flow communication between the pumping mechaniεm and the patient*ε peritoneal cavity, an operating station for the casεette including a holder for receiving the caεεette body, and preεεure tranεfer meanε within the holder operative, when the caεεette iε received within the holder, for applying pneumatic preεεure to the diaphragm to draw liquid into the pump chamber and to expel liquid from the pump chamber, and firεt meanε for deriving an initial air volume meaεurement V 1 after conveying pneumatic preεεure to draw liquid into the pump chamber and for deriving a final air volume meaεurement V f after conveying pneumatic preεεure to expel liquid from the pump chamber, the firεt meanε including a reference chamber having a known volume V, carried within the holder and, like the preεεure tranεfer meanε, expoεed to generally the εame temperature conditionε aε the pumping mechaniεm, meanε for controlling communication between the reference chamber and the preεεure transfer means by, when liquid ie drawn into the pump chamber and liquid iε expelled from the pump chamber, cloεing communication between reference chamber and the preεεure tranεfer meanε to initialize the reference chamber to a meaεured initial air preεεure (IP #1 ) while conveying a meaεured preεεure to the preεεure tranεfer meanε ( IP i) ' (ϋ) then opening communication between the reference chamber and the preεεure tranefer meanε to allow preεεure equilibration at a meaεured new air pressure in the preεεure tranεfer meanε (IP^) and a measured new air presεure in the reference chamber ( IP . 2 ) » and (ϋi) then deriving the air volume meaεurement V 1 or V aε followε: V 1 or f - CIB.1 - IP.a ) * V.- (IP^ - IP dl ) and second meanε for deriving a meaεurement of liquid volume delivered (V d ) by the pumping chamber aε followε: V d - V f - v t . 2. A system according to claim 1 wherein the first meanε further includeε meanε for applying a temperature correction factor (F t ) to the known volume of the reference chamber V, to derive a temperature-corrected reference volume V, t , aε followε: and wherein the second meanε deriveε the liquid volume meaεurement V: V - (IP. 2 - IP. * V, t _ (IP^ - IP dl ) 3. A εystem according to claim 2 wherein the means for applying a temperature correction factor (F t ) includeε means for sensing the temperature of the reference chamber and means for sensing the temperature of the pump chamber so that where: C t is the sensed absolute temperature of the pumping chamber (expresεed in degreeε Rankine or Kelvin) , and R t iε the sensed absolute temperature of the reference chamber (expresεed in the same units as C t ) . 4. A system according to claim 1 wherein the reference chamber carries within it an insert for dampening pneumatic presεure. 5. A εyεtem according to claim 4 wherein the inεert iε made of an open cell porouε material. 6. A εyεtem according to claim 4 wherein the inεert includeε a heat conducting material. 7. A method for performing peritoneal dialyεiε compriεing the εtepε of eεtabliεhing flow communication with the patient'ε peritoneal cavity through a pumping mechaniεm that compriεeε a pump chamber and a diaphragm, and emulating a selected gravity flow condition by applying pneumatic presεure to the diaphragm through an actuator to operate the pump chamber to draw dialyεiε liquid into the pump chamber and to expel dialyεiε liquid from the pump chamber to either move dialyεiε liquid from the peritoneal cavity or move dialyεiε liquid into the peritoneal cavity, and deriving a meaεurement of liquid volume pumped through the pump chamber by deriving an initial air volume meaεurement V t after operating the actuator to draw liquid into the pumping chamber; deriving a final air volume meaεurement V f after operating the actuator to expel liquid from the pumping chamber; and deriving the liquid volume delivered (V d ) by the pumping chamber aε followε: d - V f - V,, and wherein V t and V £ are derived by controlling communication between a reference chamber having a known air volume V, and the actuator by: (i) applying a temperature correction factor (F t ) to the known volume of the reference chamber V, to derive a temperature-corrected reference air volume V, t , aε followε: V. t «= F r * V. (ii) when liquid iε either drawn into or expelled from the pump chamber, cloεing communication between reference chamber and the actuator to initialize the reference chamber to a meaεured initial air preεsure (l p .ι) while applying a measured pressure to the actuator (IP dl ) ; (iii) opening communication between the reference chamber and the actuator to allow pressure equilibration at a measured new air preεεure in the actuator (IP^) and a meaεured new air preεεure in the reference chamber (IP, 2 ) and (iv) deriving the air volume meaεurement V L or V f as follows: t „ £ - (IP S1 - IP. 2 ) * v tt _ (»„ - IP dl ) 8. A method according to claim 7 wherein the step of applying a temperature correction factor (F t ) includes the εtepε of sensing the temperature of the reference chamber, and sensing the temperature of the pump chamber so that where: C t is the sensed absolute temperature of the pumping chamber (expreεεed in degrees Rankine or Kelvin) , and ^ is the sensed absolute temperature of the reference chamber (expreεsed in the same units aε C t ) . 9. A method for deriving the volume of liquid pumped through a pumping chamber that iε operated in reεponεe to pneumatic pressure variations applied by a pump actuator compriεing the etepε of drawing a volume of liquid to be pumped into the pumping chamber by applying negative preεεure to the pump actuator, deriving an initial air volume V L by retaining the initial liquid volume in the pumping chamber, initializing a reference chamber having a known air volume V, to a meaεured initial air preεεure (IP sl ) , the reference chamber being firεt iεolated from the pump actuator, applying a temperature correction factor (F t ) to the known air volume of the reference chamber V, to derive a temperature-corrected reference air volume V, c , aε follows: applying positive presεure to the pump actuator and meaεuring thiε air preεεure (IP dl ) , opening communication with the reference chamber to allow preεεure equilibration and meaεuring the new air preεεure in the pump actuator (IP^) and the new air preεεure in the reference chamber (IP s2 ) , calculating V 1 aε followε: V, - CEP.! - IP. a ) * V. t - (IP^ - IP dl ) expelling the volume of liquid from the pumping chamber by applying poεitive preεεure to the pump actuator, deriving a final air volume V £ by: retaining the final liquid volume in the pumping chamber, again initializing the reference chamber a measured initial air pressure (FP tl ) , having firεt isolated the reference chamber from the pump actuator chamber, again applying positive presεure to the pump actuator and meaεuring thiε air preεεure (FP dα ) , again opening communication with the reference chamber to allow equilibration and meaεuring the new air preεεure in the pump actuator (FP d2 ) and the new air preεεure in the reference chamber (FP, 2 ) , calculating V A aε followε: V, = (FP. - FP >2 ) * V, t _ (FP^ - FP dl ) deriving the liquid volume delivered (V d ) aε followε: V d - V £ - V, 10. A method according to claim 9 wherein and where: C ς is the sensed absolute temperature of the pumping chamber (expresεed in degreeε Rankine or Kelvin) , and R-. iε the εensed temperature of the reference chamber (expresεed in the εame unitε aε 11. A peritoneal dialysiε system comprising a pumping mechanism comprising a diaphragm, means for establishing flow communication with the patient's peritoneal cavity through the pumping mechanism, and actuating means for emulating a selected gravity flow condition by applying pneumatic pressure to the diaphragm to operate the pumping mechanism to either move dialysiε liquid from the peritoneal cavity or move dialysiε liquid into the peritoneal cavity, and control meanε εelectively operating the actuating meanε for applying pneumatic preεεure to emulate either a fixed head height condition or different head height conditionε, and meanε for deriving a meaεurement of liquid volume moving through the pumping mechanism including a reference chamber having a known air volume V,, an insert occupying the reference chamber for dampening pneumatic presεure, meanε controlling communication between the reference chamber and the actuating meanε being operable for (i) cloεing communication between reference chamber and the actuating meanε to initialize the reference chamber to a meaεured initial air preεεure (IP. while applying a meaεured air preεεure to the actuating meanε (IP dl ) and (ii) opening communication between the reference chamber and the actuating meanε to allow preεεure equilibration at a meaεured new air preεεure in the actuating meanε (IP 2 ) and a meaεured new air preεεure in the reference chamber (IP, 2 ) , and meanε for deriving an air volume meaεurement V aε followε: V - CEP., - 1P, 2 ) * V_ (IP-u - IP dl ) wherein the meanε for deriving a meaεurement of liquid volume moving through the pumping mechanism further includes meanε for deriving an initial air volume meaεurement V L upon operating the actuating meanε to draw liquid into the pumping mechanism, means for deriving a final air volume measurement V £ upon operating the actuating means to expel liquid from the pumping mechanism, and means for deriving liquid volume delivered ( v a ) by the pumping mechaniεm aε followε: V d «= V f - V, 12. A system according to claim 11 wherein the actuating means includeε an actuating chamber for receiving pneumatic preεεure and an inεert occupying the actuating chamber for dampening pneumatic preεεure. 13. A system according to claim 12 wherein the insert in the actuating chamber is made of an open cell porouε material. 14. A system according to claim 11 wherein the insert in the reference chamber is made of an open cell porous material.

Inventors: BRYANT ROBERT J, KAMEN DEAN, LANIGAN RICHARD, SPENCER GEOFFREY P, VILLENEUVE RICHARD R, VINCENT DOUGLAS E, BRYANT, ROBERT, J., KAMEN, DEAN, LANIGAN, RICHARD, SPENCER, GEOFFREY, P., VILLENEUVE, RICHARD, R., VINCENT, DOUGLAS, E.
Applicants: DEKA PRODUCTS LP, DEKA PRODUCTS LIMITED PARTNERSHIP
Application year: 1994
Main classification: A61M1
IPC codes: A61M1, A61M5, G01F1, G01F15